MnCePrO2-δ复合氧化物在O2及NOx气氛中对柴油机颗粒的氧化活性研究

将采用自蔓延高温燃烧合成法(SHS)制备的一系列MnCePrO2-δ复合氧化物催化剂以及贵金属Pt催化剂涂覆于空白的DPF载体上,对其同时去除柴油机尾气中碳烟颗粒物和氮氧化物反应的催化活性进行研究。结果表明: MnCePrO2-δ系列催化剂在氧化碳烟颗粒物和NO的性能上相较于贵金属Pt有明显的优势。其中,Mn0.3Ce0.5Pr0.2具有最好的催化活性,催化去除碳烟颗粒的起燃温度为296 ℃,最大氧化碳烟颗粒速率温度为418 ℃,NO的转化率达到65.6%。利用程序升温反应技术研究了气体流量和加载碳烟质量的变化对Mn0.3Ce0.5Pr0.2催化剂催化活性的影响。研究表明:当气体流量由500(mL· min-1)减小至100(mL· min-¹)时,碳烟颗粒的起燃温度和最大氧化速率温度分别降低了10 ℃和20 ℃,而加载的碳烟质量的改变对碳烟颗粒的起燃温度和最大氧化速率温度没有影响。     

NOx对La1-xMxMnO3催化氧化碳烟活性影响的研究

采用铯、钾、铈(Cs、K、Ce)部分取代镧(La)制备了La1-xMxMnO3催化剂,并分析了催化剂的比表面积和晶格结构。在O2、NO O2、NO2 O2三种不同的气体氛围下开展了碳烟、碳烟 催化剂的程序升温氧化试验,考察NOx对碳烟催化氧化活性的影响。研究结果表明,NOx的存在显著促进了碳烟的催化氧化,各特征温度降幅均在100 K左右,NO2的影响强于NO,但与无催化剂时相比,两者的差距明显缩小,这主要是由于NOx在催化剂表面可发生氧化还原循环反应。NOx存在并未影响催化剂活性的排序,Cs取代催化剂的活性依然最高,NO存在时碳烟的起燃温度、峰值温度和燃尽温度降低到618 K、667 K和706 K,NO2存在时碳烟的起燃温度、峰值温度和燃尽温度降低到592 K、657 K和679 K。初步分析了NOx存在时碳烟催化氧化的机理。     

氟掺杂VOx/TiOy低温选择性催化还原催化剂的制备及其性能

通过溶胶一凝胶法制得氟掺杂氧化钛载体,然后负载活性组分氧化钒,制得了不同氟掺杂量的氧化钒/氧化钛催化剂,并对这些催化剂进行了活性测试和表征.结果表明:氟掺杂能大幅度提高催化剂的低温选择性催化还原(SCR)性能,且氟掺杂量为[F]/[Ti]=1.35×10-2时,催化活性最好;在453 K时,该催化荆对NO的脱除效率为61%,在483 K时,NO的脱除效率为97%;SO2和H2O对氟掺杂催化剂上的低温SCR反应存在协同抑制效应,且该抑制效应是可逆的;催化剂活性得到提高的原因在于,氟掺杂增强了活性组分氧化钒与载体氧化钛之间的相互作用,有利于提高催化剂的氧化还原性能,同时促进了超氧自由基的形成,有利于中间产物NO2和NO3-的生成.     

DOC/DOC+CDPF对重型柴油机气态物排放特性的影响研究

基于AVL-PEUS傅里叶变换红外光谱仪(FTIR)研究柴油机氧化型催化器(DOC)、柴油机氧化型催化器耦合催化型颗粒捕集器(DOC+CDPF)对重型柴油机一氧化碳(CO)、总碳氢化合物(THC)、一氧化氮(NO)、二氧化氮(NO_2)和二氧化硫(SO_2)气态物排放特性的影响。研究结果表明:相比单独的DOC,DOC+CDPF对CO具有更低的起燃温度,在催化剂活性位上THC比CO具有较强的吸附强度和活性位竞争优势,因此具有比CO更低的起燃温度;DOC和DOC+CDPF均能不同程度地减少NO、增加NO_2、减少总NO_x排放,减少NO的主要途径是氧化机理;在催化剂中添加氧化铈(CeO_2)能有效实现稀燃储硫、富燃释放硫的效果,增强催化剂的抗硫能力。     

掺混PODE对DOC+CDPF氧化及再生特性的影响

在高压共轨柴油机上研究了使用掺混20%聚甲氧基二甲醚的柴油(D80P20)对搭载柴油氧化型催化器(DOC)和催化型颗粒捕集器(CDPF)的后处理装置(DOC+CDPF)的影响,包括小负荷时的低温氧化特性和大负荷时的颗粒物加载和再生特性.研究表明:小负荷工况下在1400~2000 r/min内,DOC和DOC+CDPF对柴油排放的CO转化效率平均分别高达70%和90%,而对D80P20排放的CO转化效率则仅近19%和36%,燃用柴油时DOC和CDPF后端的排气升温现象较为明显,低温氧化特性优于D80P20;在大负荷低速工况下,燃用D80P20时,DOC前/后两端排气氧质量分数以及NO2排放均明显高于柴油,但CO原始排放和不透光烟度显著低于柴油.因而DOC+CDPF对D80P20的CO、PM氧化放热量较低,DOC后端温升明显低于柴油.此外,大负荷下DOC+CDPF对D80P20排放的CO净化效率和PM氧化再生效率高达近100%,DOC+CDPF前/后端压差峰值仅是柴油的1/3,其可显著降低CDPF的堵塞风险,减少主动再生频率.     

Pd和K共负载的Mg-Al水滑石基氧化物同时去除碳烟和NO_x

采用浸渍法将Pd和K共同负载到Mg-Al水滑石基氧化物(Pd-K/MgAlO)上,用于碳烟颗粒和NOx的同时去除,并与Pd/MgAlO和K/MgAlO催化剂进行了比较.研究发现,单独的Pd负载不具备催化碳烟燃烧的活性,但可以提高生成CO2的选择性;引入NOx后,Pd可以通过促进NO氧化对碳烟燃烧有所改善,同时可以去除少量的NOx.当Pd与K共负载时,碳烟燃烧温度显著降低;引入NOx后,起燃温度进一步降低至240,℃左右,而且碳烟燃烧受接触方式的影响不大,其中催化作用的主要影响组分是K.在Pd和K协同作用下,NOx的最大去除效率达到45%,高于Pd/MgAlO和K/MgAlO的去除效率.其中,一部分NOx被碳烟还原,另一部分则发生了分解反应.     

催化型颗粒捕集器配方对柴油机颗粒排放特性的影响

为研究催化型颗粒捕集器(catalyzed diesel particulate filter,CDPF)配方对柴油机颗粒物净化效果的影响,基于铂/钯/铑(Pt/Pd/Rh)贵金属配方,对采用不同贵金属负载量及配比配方时的柴油机颗粒排放特性进行了试验研究。研究结果表明:当CDPF催化剂配方中贵金属负载量较高时,柴油机颗粒物质量浓度降幅较大,平均降幅达97%;当催化剂配方中钯元素含量较高时,颗粒物数量浓度降幅较大,平均降幅达98%,采用钯元素含量较高的催化剂配方,对核态颗粒物的净化效果较明显。     

纳米级V_2O_5/TiO_2的活性特征及对碳烟氧化的催化作用

采用浸渍法制备了不同钒负载量的纳米级V_2O_5/TiO_2催化剂,通过扫描电镜(scanning electron microscope,SEM)、X射线衍射仪(X-ray diffractomer,XRD)和傅里叶红外光谱(Fourier transform infrared spectrometer,FT-IR)测试手段对催化剂的物化特性进行表征。以Printex-U碳黑作为实际发动机颗粒的替代物,利用热重分析法探究V_2O_5负载量对催化氧化碳烟活性的影响,并基于Flynn-Wall-Ozawa法定量表征碳烟催化氧化反应过程。研究结果表明:较低钒负载量时,活性组分钒氧物种处于高度分散状态,基本呈现单层分布。当负载量较高(40%)时,部分钒氧物种开始团聚并以结晶态析出,催化剂表面出现明显的柱状晶结构。随着钒负载量的增加,在碳烟氧化过程中催化剂活性呈递增趋势。在一系列样品中,负载量20%的V_2O_5/TiO_2催化剂表现出最佳催化活性,与无触媒状态相比,碳烟氧化的起燃温度Ti、失重峰值温度Tp和燃尽温度Tf等特征温度的降幅最大。当负载量达40%时,V_2O_5主要以结晶相存在,占据大量活性位,降低催化效果。由FWO法热力学分析得到颗粒氧化的活化能的顺序为EPMEV5EV10EV40EV20。     

柴油机排气的O2-NO2对碳烟氧化的协同效应

柴油机排气温度低于873 K时难以直接氧化碳烟,使得柴油机颗粒捕集器（DPF）要实现低温、高效率的再生面临严峻考验．为了明确DPF内O₂-NO₂快速氧化碳烟的反应机制,基于量子化学与化学动力学,采用微观机理结合宏观分析的手段,探究了O₂-NO₂协同氧化碳烟的机理,并对碳烟的氧化进行定性与定量分析．研究表明：O₂-NO₂对碳烟的活性位有竞争吸附作用,NO₂的吸附能明显高于O₂,但O₂与碳烟更易形成C（O）及活性O*.NO₂易与O₂产生的C（O）反应,生成的NO3-可有效氧化活性C*,实现O₂-NO₂对碳烟氧化的协同效应;中等温度为742 K时,O₂与芘基（A4-）反应生成A4O的量保持最多,且O₂与NO₂摩尔分数比为1/2时,A4-的10 s...     

模拟碳烟在CDPF过滤壁面上的氧化演变特性

基于可视化单通道沉积/再生试验台架,利用固体颗粒发生器对催化型柴油机颗粒捕集器(CDPF)载体切片进行颗粒沉积,激光位移传感器在线测量过滤壁面上颗粒层厚度的变化趋势,耦合压降变化规律,结合过滤表面的扫描电子显微镜图(SEM),探索再生时CDPF切片上颗粒层的氧化演变规律.试验结果表明:再生时CDPF/非催化型(DPF)切片上的颗粒层压降呈现三阶段的变化趋势.再生第Ⅰ阶段,DPF和CDPF的颗粒层压降下降率分别为0.23 Pa/s和0.61 Pa/s,且对应颗粒层厚度的相对占比CDPF比DPF高16%,SEM图观测到CDPF第Ⅰ阶段末期出现少量的有效通孔;第Ⅱ阶段,DPF和CDPF颗粒层压降下降率分别为0.42 Pa/s和1.74 Pa/s,其对应颗粒层厚度的相对占比分别为54%和38%,SEM图观测到CDPF微孔中碳黑燃烧完全,有效通孔增至整个载体切片表面;第Ⅲ阶段,CDPF的催化效果不明显,CDPF和DPF压降变化均逐渐趋于水平,颗粒层厚度值呈现波动.     

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.     

Contents in Volume 23,2014

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Performance assessment of some ice TES systems

In this paper, a performance assessment of four main types of ice storage techniques for space cooling purposes, namely ice slurry systems, ice-on-coil systems (both internal and external melt), and encapsulated ice systems is conducted. A detailed analysis, coupled with a case study based on the literature data, follows. The ice making techniques are compared on the basis of energy and exergy performance criteria including charging, discharging and storage efficiencies, which make up the ice storage and retrieval process. Losses due to heat leakage and irreversibilities from entropy generation are included. A vapor-compression refrigeration cycle with R134a as the working fluid provides the cooling load, while the analysis is performed in both a full storage and partial storage process, with comparisons between these two. In the case of full storage, the energy efficiencies associated with the charging and discharging processes are well over 98% in all cases, while the exergy efficiencies ranged from 46% to 76% for the charging cycle and 18% to 24% for the discharging cycle. For the partial storage systems, all energy and exergy efficiencies were slightly less than that for full storage, due to the increasing effect wall heat leakage has on the decreased storage volume and load. The results show that energy analyses alone do not provide much useful insight into system behavior, since the vast majority of losses in all processes are a result of entropy generation which results from system irreversibilities.     

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%.     

Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H₂ yield. The results demonstrated that the optimal culture conditions for the highest H₂ production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m^?2 s^?1. Under these conditions, the maximal H₂ yield was 255 μmol mg^?1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H₂ yield included decreased O₂ content, enhanced algal growth, and increased H₂ase activity and starch content of the combined system.     

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.     

Natural-gas fueled spark-ignition (SI) and compression-ignition (CI) engine performance and emissions

Natural gas is a fossil fuel that has been used and investigated extensively for use in spark-ignition (SI) and compression-ignition (CI) engines. Compared with conventional gasoline engines, SI engines using natural gas can run at higher compression ratios, thus producing higher thermal efficiencies but also increased nitrogen oxide (NO_x) emissions, while producing lower emissions of carbon dioxide (CO₂), unburned hydrocarbons (HC) and carbon monoxide (CO). These engines also produce relatively less power than gasoline-fueled engines because of the convergence of one or more of three factors: a reduction in volumetric efficiency due to natural-gas injection in the intake manifold; the lower stoichiometric fuel/air ratio of natural gas compared to gasoline; and the lower equivalence ratio at which these engines may be run in order to reduce NO_x emissions. High NO_x emissions, especially at high loads, reduce with exhaust gas recirculation (EGR). However, EGR rates above a maximum value result in misfire and erratic engine operation. Hydrogen gas addition increases this EGR threshold significantly. In addition, hydrogen increases the flame speed of the natural gas-hydrogen mixture. Power levels can be increased with supercharging or turbocharging and intercooling. Natural gas is used to power CI engines via the dual-fuel mode, where a high-cetane fuel is injected along with the natural gas in order to provide a source of ignition for the charge. Thermal efficiency levels compared with normal diesel-fueled CI-engine operation are generally maintained with dual-fuel operation, and smoke levels are reduced significantly. At the same time, lower NO_x and CO₂ emissions, as well as higher HC and CO emissions compared with normal CI-engine operation at low and intermediate loads are recorded. These trends are caused by the low charge temperature and increased ignition delay, resulting in low combustion temperatures. Another factor is insufficient penetration and distribution of the pilot fuel in the charge, resulting in a lack of ignition centers. EGR admission at low and intermediate loads increases combustion temperatures, lowering unburned HC and CO emissions. Larger pilot fuel quantities at these load levels and hydrogen gas addition can also help increase combustion efficiency. Power output is lower at certain conditions than diesel-fueled engines, for reasons similar to those affecting power output of SI engines. In both cases the power output can be maintained with direct injection. Overall, natural gas can be used in both engine types; however further refinement and optimization of engines and fuel-injection systems is needed.     

Exergetic evaluation of 5 biowastes-to-biofuels routes via gasification

This paper presents the exergy analysis results for the production of several biofuels, i.e., SNG (synthetic natural gas), methanol, Fischer–Tropsch fuels, hydrogen, as well as heat and electricity, from several biowastes generated in the Dutch province of Friesland, selected as one of the typical European regions. Biowastes have been classified in 5 virtual streams according to their ultimate and proximate analysis. All production chains have been modeled in Aspen Plus in order to analyze their technical performance. The common steps for all the production chains are: pre-treatment, gasification, gas cleaning, water–gas-shift reactions, catalytic reactors, final gas separation and upgrading. Optionally a gas turbine and steam turbines are used to produce heat and electricity from unconverted gas and heat removal, respectively. The results show that, in terms of mass conversion, methanol production seems to be the most efficient process for all the biowastes. SNG synthesis is preferred when exergetic efficiency is the objective parameter, but hydrogen process is more efficient when the performance is analyzed by means of the 1st Law of Thermodynamics. The main exergy losses account for the gasification section, except in the electricity and heat production chain, where the combined cycle is less efficient.     

Controls on the Karaha–Telaga Bodas geothermal reservoir,Indonesia

Karaha–Telaga Bodas is a partially vapor-dominated, fracture-controlled geothermal system located adjacent to Galunggung Volcano in western Java, Indonesia. The geothermal system consists of: (1) a caprock, ranging from several hundred to 1600 m in thickness, and characterized by a steep, conductive temperature gradient and low permeability; (2) an underlying vapor-dominated zone that extends below sea level; and (3) a deep liquid-dominated zone with measured temperatures up to 353 °C. Heat is provided by a tabular granodiorite stock encountered at about 3 km depth. A structural analysis of the geothermal system shows that the effective base of the reservoir is controlled either by the boundary between brittle and ductile deformational regimes or by the closure and collapse of fractures within volcanic rocks located above the brittle/ductile transition. The base of the caprock is determined by the distribution of initially low-permeability lithologies above the reservoir; the extent of pervasive clay alteration that has significantly reduced primary rock permeabilities; the distribution of secondary minerals deposited by descending waters; and, locally, by a downward change from a strike-slip to an extensional stress regime. Fluid-producing zones are controlled by both matrix and fracture permeabilities. High matrix permeabilities are associated with lacustrine, pyroclastic, and epiclastic deposits. Productive fractures are those showing the greatest tendency to slip and dilate under the present-day stress conditions. Although the reservoir appears to be in pressure communication across its length, fluid, and gas chemistries vary laterally, suggesting the presence of isolated convection cells.     

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.