多碟太阳能聚热与生物质超临界水气化耦合制氢

搭建了一套连续式多碟太阳能聚热与生物质超临界水气化耦合制氢系统,以生物质模型化合物(乙二醇、丙三醇、葡萄糖)为原料在该装置上进行了气化制氢实验,研究了太阳能直接辐照度(DNI)、物料成分、物料浓度、停留时间对气化效果的影响。实验结果表明:太阳能直接辐照度对太阳能吸收器腔内及反应器壁温的影响较大,进而能影响气化效果,在实验流量、压力范围内当DNI为363～656W/m2时,反应器出口流体温度达520～676℃,可以满足生物质超临界水气化制氢的温度及能量需要。0.1mol/L葡萄糖气化H2体积分数均值超过50%,H2产量为27.2mol/kg,气化率达109.7%。低物料浓度和长停留时间有利于气化效果的提高。实验验证了利用可再生的太阳能聚焦供热耦合生物质超临界水气化制氢是可行的。     

玉米芯在超临界水中气化制氢实验研究

以玉米芯为原料,羧甲基纤维素纳(CMC)为添加剂,利用连续管流反应器,在反应压力为22.5MPa~27.5MPa、反应器壁温为550℃~650℃、反应停留时间为0.33min~0.67min、物料浓度为3wt%~6wt%的条件下,对玉米芯超临界水气化制氢进行了实验研究。利用正交实验设计与分析方法,得到实验条件范围内玉米芯超临界水气化制氢的最佳反应参数,同时对气化过程主要操作参数的影响进行了分析。实验表明温度对气化影响最大,高温度有利于产氢,气化制氢的最佳压力为25MPa,反应停留时间越长气化越完全,低浓度生物质比高浓度生物质更容易气化。     

木质素在超临界水中气化制氢的实验研究

以木质素为原料,利用连续管流反应器,首先在反应压力为15.0～27.5MPa、反应器壁温为500～650℃、物料流速为4.7～7.5mL/min的条件下,对质量浓度为1%～3%的木质素在超临界水中进行了气化制氢的实验研究。针对实验中存在的问题,改造了反应器,着重考查壁面温度为700～775℃下高浓度木质素的气化效果。实验表明升高壁温能够极大提高木质素在超临界水中的气化效果,700℃以上木质素可以高效气化;升高压力有利于氢气质量产率的提高,并可促进甲烷化反应;而高浓度不利于木质素气化;降低流速,有利于提高氢气质量产率,但对气态产物中各组分气体的体积百分含量影响不大;相同条件下,木质素较纤维素更难气化,气化率较低。     

连续式超临界水中煤/CMC催化气化制氢

在向水煤浆中添加CMC（羧甲基纤维素钠），成功实现水煤浆高压均匀输送基础上，对超临界水中煤／CMC催化气化制氢性能进行了进一步研究。结果表明：在压力20～25MPa、停留时间15～30s、NaOH添加量0．1％、反应器外壁温650℃条件下，超临界水中煤/CMC催化气化制氢气体产物中H2摩尔含量远比常规气化高，主要气体产物是H2、CO2和CH4。增加物料中CMC的含量、升高压力均有利于提高气体产物中心的产量，延长停留时间虽有利于物料气化但不利于氢气的制取。     

生物质超临界水气化制氢反应建模及数值模拟

建立了管式反应器中生物质超临界水气化制氢反应的数学模型,同时提出了以葡萄糖做为生物质模型化合物的全局气化反应动力学模型。模型计算结果与实验值的比较表明该模型能较好的预测反应器出口温度与气体产物组份分布。利用该模型数值模拟计算得到了反应器中温度场、速度场基本情况以及化学反应速率分布的基本规律。该文通过计算还讨论了反应器入口水温、反应器壁温以及物料和预热水之比对反应器内气化反应的影响,得出一系列重要结论。该模型对生物质超临界水反应器系统的优化设计与化学反应最佳工况的选择有一定的实用价值。     

生物质超临界水催化气化制氢实验系统

生物质超临界水催化气化制氢是一项很有价值的离新技术，它有利于开发广泛的生物质资源，为大规模的制氢提供一条高效、清洁的途径。针对生物质超临界水气化制氢，国内外结合工作具体要求和条件，设计出了一系列生物质超临界水催化气化制氢的实验系统。主要对国内外几种较好的生物质超临界水催化气化制氢实验进行了综合评述，分析了各类实验系统存在的问题及待改进之处。     

生物质流化床气化技术应用研究现状

按所得产品不同,可将生物质气化技术分为制氢、发电和合成液体燃料3大类。文章介绍了生物质流化床水蒸气气化制氢、催化气化制氢和超临界水气化制氢的工艺特点;分析了生物质流化床气化发电的技术、经济可行性;简述了生物质流化床气化合成液体燃料的研究现状;指出气化产出气化学当量比调变、焦油去除问题和合成气净化是生物质流化床气化技术应用的主要瓶颈,认为定向气化是今后研究的主要方向。     

生物质无氧气化制氢系统的热力学计算

介绍了一种基于CO_2接受体气化法的生物质无氧气化制氢系统。采用热力学平衡模型,研究了以玉米秸这一典型生物质为原料时系统压力、温度、[H_2O]/[C]比、[Ca]/[C]比对制氢过程的影响规律。获得典型工况下,系统制氢效率对这几个参数的相对线性敏感性系数。结果表明,H_2浓度在一定范围内随压力升高而明显增大,同时H_2产量会有少量降低,过高的温度会明显降低H_2产量及浓度。综合考虑,合适的气化压力在1.3～2.5MPa之间,不同压力具有不同适合制氢的最高温度。[H_2O]/[C]比的提高可以促进H_2生成,但大于1.5之后,H_2浓度明显下降,合适的[H_2O]/[C]比在1.5～2.0之间。[Ca]/[C]比的增加有利于H_2产量及浓度的提高。线性敏感性系数的计算表明,计算工况下[H_2O]/[C]比对制氢效率的影响非常大,压力和温度的影响也比较显著,[Ca]/[C]比的影响为零。     

串行流化床生物质气化制氢试验研究

基于串行流化床生物质气化技术,以水蒸气为气化剂,在串行流化床试验装置上进行生物质气化制氢的试验研究,考察了气化反应器温度、水蒸气/生物质比率(S/B)对气化气成分、烟气成分和氢产率的影响。结果表明:在燃烧反应器内燃烧烟气不会串混至气化反应器,该气化技术能够稳定连续地从气化反应器获得不含N_2的富氢燃气,氢浓度最高可达71.5%;气化反应器温度是影响制氢过程的重要因素,随着温度的升高,气化气中H_2浓度不断降低,CO浓度显著上升,氢产率有所提高;S/B对气化气成分影响较小,随着S/B的增加,氢产率先升高而后降低,S/B的最优值为1.4。最高氢产率(60.3g H_2/kg biomass)是在气化反应器温度为920℃,S/B为1.4的条件下获得的。     

超临界水中生物质气化制氢的反应路径

超临界水中生物质气化制氢技术因其具有良好的环保性、产氢高等特点已成为氢能领域的研究热点之一。文中对超临界水中生物质气化制氢反应路径的研究结果进行了总结，归纳了生物质及其模型化合物葡萄糖在亚临界和超临界水中分解气化的可能的反应路径以及反应过程中产生的一系列中间产物，讨论了影响反应的主要因素。     

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.     

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.     

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.     

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.     

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.     

液压系统常见的故障诊断及处理

任何工程机械式液压设备使用时出现故障是不可避免的。但是怎样确定故障的原因及找到好的解决方法,这是使用者最关心的问题。讲述了液压系统常见的故障及其排除方法。     

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.