微小固体颗粒气力输送固气比试验研究

对微小固体颗粒在密相气力输送情况下进行试验,研究输送压力最高可达0.5 MPa的输送过程中,输送系统的罐压、背压和粉量调节阀的开度以及流化风量和载气流量分别对固气比的影响。结果表明:差压增大会导致固气比增大;粉量调节阀开度增大,有助于固气比提高;适当增大流化风量或载气流量可提高固气比,达到峰值后,固气比会随着流化风量或载气流量的增大而减小,固气比达到峰值时对应的流化风量、载气流量为最佳值。     

高压浓相粉煤气力输送试验研究

在输送压力可达4.0 MPa,固气比高达500 kg/m3的高压气力输送试验台上,用氮气进行粉煤高压浓相气力输送试验研究。分别在不同的输送差压、充压风量和流化风量等条件下进行了输送试验,考察操作参数对煤粉质量流量和固气比等气力输送特征参数的影响。结果表明,煤粉的质量流量随着输送差压和充压风量的增大而增大;输送压力越高,差压的变化对煤粉的质量流量的影响越显著;固气比随着输送差压和充压风量的升高而增加,随着流化风量的增大先增大后减小;输送压力越高,固气比越大;保持进入发料罐的气体总量不变,当Qf<0.55 m3/h时,充压风量的变化对输送参数的影响主导作用,当Qf>0.55 m3/h时,流化风量的变化对输送参数的影响较大。     

高压超浓相气力输送固气比研究

在输送压力可达3.7 MPa,固气比可达660 kg·m-3的气力输送实验台上进行系统的研究,考察输送压力、输送差压、流化风量、充压风量、补充风量、煤粉含水率等条件对固气比的影响.采用改进学习算法的BP神经网络,对固气比进行有效预测.结果表明,固气比随着输送差压的增大而增大;随着流化风量的增大先增大后减小;注入风量一定时,充压风量增大固气比先减小后增大;固气比随着补充风量的增大而显著减小;随着煤粉含水率的增大而减小;随着表观气速的增大而减小.获得了系统最佳的操作条件.建立的BP网络,最大训练误差为2.7%,最大预测误差为5.8%,具有很好训练结果和预测能力.     

粉煤加压密相输送特性试验研究

在压力可达4.0 MPa,固气比高达500 kg/m3的气力输送试验台上进行粉煤输送试验.分别在不同的输送差压、充压风量和流化风量等条件下进行了输送试验,考察操作参数对煤粉质量流量和固气比等气力输送特征参数的影响.结果表明,煤粉的质量流量随着输送差压和输送风量的增大而增大;固气比随着输送差压和充压风量的升高而增加,随着流化风量的增大先增大后减小;总风量不变时,当Qf＜0.7m3/h时,充压风量的变化对输送参数的影响起主导作用,当Qf＞0.7 m3/h时,流化风量的变化对输送参数的影响较大.     

高压密相气力输送固相流量的实验与GRNN网络预测

煤粉高压密相气力输送是气流床加压气化的关键技术之一.在输送压力可达3.7 MPa,管路固气比可达660 kg/m3的气力输送实验台上进行系统的研究,考察输送压力、输送差压、流化风量、充压风量、补充风量、煤粉含水率等条件对固相质量流量的影响.结果表明:固相流量随着输送差压的增大而增大;随着流化风量的增大而先增大后趋向于某一定值;注入风量一定时,随着充压风量的增大而先减小后增大;与补充风量的大小基本无关;随着煤粉含水率的增大而减小.同时建立广义回归神经网络(GRNN)对固相流量进行了有效预测,最大预测误差在2.3%以内.上述工作将为系统的控制和运行提供一定的指导,同时为深化高压密相气力输送的研究奠定基础.     

煤粉高压超浓相气力输送的实验研究

煤粉的高压超浓相气力输送是大规模煤气化技术的关键技术之一.在输送压力可达4MPa、管路固气比可达660 kg/m3的气力输送实验台上进行实验,考察不同的输送压力、输送差压、流化风量、充压风量、补充风量、煤粉含水率等条件对煤粉质量流量、固气比、表观气速等输送特性参数的影响.结果表明:采用较高的输送压力、较大的差压、合理的风量与含水率较低的煤粉更有利于实现高压超浓相的气力输送.     

生物质粉末的气力输送能力实验研究

在生物质的气化流程中,由于生物质粉末本身的理化特性,使得对于生物质的气力输送面临着许多的挑战。为降低输送成本,搭建了能够连续可靠运行的生物质粉末(锯末)气力输送实验台。研究不同流化风流量、载气风流量、罐压、背压下生物质原料气力输送特性,以及固相质量流量的相关变化规律。通过对前人所提出的气力输送模型进行研究,并得到了气力输送的固相质量流量多元回归公式,经与实验数据比对,具有良好的匹配性较好的预测效果。     

不同平均粒径煤粉的高压密相气力输送

在高压密相气力输送试验台上,进行了不同平均粒径煤粉的密相输送试验.分析了总输送差压和流化风量对不同平均粒径煤粉输送特性的影响,以及水平管和水平弯管的阻力特性.结果表明:增加总输送差压或者流化风量,煤粉的体积分数都经历了一个先增大后减小的过程;系统的输送能力随着煤粉平均粒径的增大而降低;在相同表观气速及煤粉质量流量下,平均粒径大的煤粉压损大于平均粒径小的煤粉压损;输送相同质量流量煤粉时,水平弯管的压损大于水平管,且水平弯管与水平管压损的比值随着煤粉质量流量的增加而增大.     

浓相粉煤灰气力输送差压波动ARMA功率谱分析

在料罐体积均为0．6m^3,输送管内径为20mm,输送距离为20m的试验台上进行浓相气力输送试验研究。采用ARMA功率谱分析输送过程中固气比对气体表观速度、压力损失和能量在频域分布的影响。结果显示：随着固气比的增加,表观速度降低,单位长度的压力损失逐渐增大,差压波动逐渐减小;功率在频域内分布随着固气比增大逐渐向低频移动,主峰峰值也随之增大。这些均与粉煤灰流动形态有关。它揭示了功率在频域内的分布情况,对研究管内运动和能量交换提供了新的研究途径。     

不同水分下煤粉高压浓相输送的试验研究

试验依托一套输送压力可达4 MPa的干煤粉加压浓相气力输送实验装置,研究煤粉含水率(M=5.45%、8.94%、12.09%、14.20%、16.20%)、输送压差、流化风流量、补充风流量对流动特性的影响。结果表明:在流化风流量和补充风流量恒定,增大输送压差,固气比随压差的增大呈现先增大后减小的趋势;而保持压差和流化风流量不变,煤粉质量流量均随补充风流量的增加而降低;系统压差和补充风流量均不变,煤粉质量流量随流化风量的增大呈现出先增大后趋于不变;维持输送压差、流化风流量和补充风流量,垂直管和水平管压降变化幅度不大,而水平弯管的压降随含水率的增大而增大,垂直弯管的压降随含水率的增大呈现先增大后减小的情况。     

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.