660MW超超临界汽轮机高压转子的高温蠕变强度分析

为了研究在高温下某660 MW超超临界汽轮机高压转子的蠕变强度,利用有限元计算方法分析了转子在额定工况下的温度和应力分布,并采用幂率模型和孔洞长大机理预测了该转子在2×105h工作中的蠕变行为,研究结果表明:在额定工况下,转子最高内应力低于屈服极限,处于纯弹性变形状态;转子内大部分区域温度在300～600℃,已进入蠕变温度范围.蠕变与热弹性耦合分析表明:蠕变会引起转子内部应力的重新分布,转子前轴封圆弧段的蠕变应变较高,而且多轴应力对该区域蠕变韧度的影响明显,应当引起足够重视.     

超超临界机组高压内缸蠕变强度分析

对某超超临界机组高压内缸的高温蠕变强度进行了研究,利用ABAQUS建立了高压内缸三维有限元模型,并进行了计算分析.结果表明:在稳态工况下高压内缸最大应力低于相应温度下材料的屈服强度,未达到屈服状态;高压内缸蠕变应变发生区域主要集中在进汽口及平衡活塞处;多轴效应对蠕变考核具有重要影响,采用多轴蠕变应变进行蠕变强度考核准确度更高;高温蠕变所引起的应力松弛使得螺栓热紧力下降,对2×105 h蠕变后的高压内缸中分面汽密性产生影响.     

超临界锅炉启动汽水分离器应力分析及数值模拟

对超临界锅炉汽水分离器变工况下的应力场进行了分析计算,探讨了在高温高压条件下蠕变变形与应力间的关系,以及存在弹性变形、塑性变形和蠕变变形时应力的计算,并使用ANASYS对某超临界锅炉汽水分离器进行了数值模拟.结果表明:在结构不连续处,即汽水分离器入口附近,局部应力最大;在机组启动初始阶段,此处的应力幅很大;而在稳定运行时,此处的应力绝对值很大,但震荡幅度很小.     

百万千瓦级汽轮机转子轮槽蠕变分析

随着汽轮机进汽参数的不断提高和机组效率的提升,转子因高温而引起的蠕变失效将演变成一个大问题而亟须解决。以某百万千瓦超超临界汽轮机中压缸转子为研究对象,采用商用软件ABAQUS,计算了在多轴应力状态下的蠕变应变,并分析了可能影响转子蠕变应变的因素。计算分析表明,在当前设计状态下,转子中心以及轮槽的蠕变应变都能满足设计要求,但转子进汽端蠕变应变对温度较为敏感。所以为了使该区域温度能更加合理的分布,需要做好整机的热力及通流设计。     

不同加卸载条件下孟底沟水电站花岗岩蠕变特性研究

针对孟底沟水电站坝区花岗岩开展了不同加卸载应力条件下的三轴蠕变试验,系统分析了不同加卸载过程中坝区花岗岩的变形特征、蠕变速率和破坏强度的变化规律,揭示了蠕变破坏模式。结果表明,孟底沟花岗岩存在蠕变应力门槛值,蠕变后期存在完整的减速、等速和加速蠕变阶段,岩石产生大量塑性变形,体积由压缩转为扩容;轴压恒定相比偏应力恒定卸围压蠕变更具时效特征,卸围压条件下出现劈裂和剪切共存的破坏模式;岩石破坏强度低于常规峰值强度,卸围压相比加轴压方式岩石强度下降幅度更大,粘聚力的降低是造成强度折减的主要因素。     

长期运行后汽轮机转子裂纹扩展行为的研究

对运行16年的30Cr1Mo1V亚临界汽轮机高中压转子进行解剖试验,采用直流电位法对材料在538℃下的蠕变裂纹、蠕变-疲劳裂纹萌生与扩展行为进行了研究,分析了不同初始应力强度因子对蠕变裂纹扩展孕育时间和蠕变裂纹扩展速率的影响,并对高温段和低温段的相关性能进行了比较,研究了不同保持时间对蠕变-疲劳裂纹扩展行为的影响,同时还分析了不同条件下裂纹扩展行为的时间或循环相关性．结果表明：疲劳缩短了蠕变-疲劳裂纹的扩展孕育期,加速了裂纹的扩展;载荷保持时间较短情况下,蠕变-疲劳裂纹扩展行为与循环相关;栽荷保持时间较长情况下,裂纹扩展行为与时间相关．     

高温环境下蠕变疲劳交互作用损伤力学研究

应力控制下的疲劳、蠕变及其交互作用损伤实际上是循环蠕变、静蠕变引起的材料延性不断耗竭的过程，本文在延性耗竭理论和损伤力学有效应力概念的基础上．对疲劳蠕变交互作用损伤演化进行了研究，提出了一个新的疲劳蠕变交互作用损伤模型．采用非弹性应变能密度变化作为损伤参量定义损伤变量。通过耐热钢1.25Cr0.5Mo光滑试样高温环境下应力控制的梯形波加载试验．验证上述疲劳蠕变交互作用模型，最终得到了1.25Cr0.5Mo钢540℃下不同最大应力、不同应力幅组合条件下的损伤演化统一表达式，试验损伤点与该模型的损伤演化规律符合较好．表明该模型和损伤变量适合于疲劳蠕变交互作用下的损伤描述．     

超超临界汽轮机转子蠕变对低周疲劳应变的影响

对某超超临界汽轮机高压转子多次启停和间隔分段稳态高温运行下的低周疲劳应变进行了全时域连续有限元计算与分析,给出了蠕变条件下低周疲劳应变的变化量级和变化图谱.结果表明:超超临界汽轮机转子低周疲劳寿命消耗需进行全时域连续计算,不能采用一次启停数据乘以启停次数的简单算法;蠕变对低周疲劳产生的影响具有长期性,但影响程度随时间逐步递减.     

汽轮机零部件多轴应力状态下的强度设计和寿命预测

介绍了汽轮机零部件多轴应力状态下的强度设计方法和低周疲劳裂纹萌生寿命预测方法,分析了汽轮机零部件多轴应力状态下稳态额定工况的极限载荷与分析设计判据,以及瞬态变工况强度的安定载荷与分析设计判据,提出了汽轮机零部件多轴应力状态下寿命预测使用的等效应力和等效应变正负号的确定方法,给出了汽轮机零部件多轴应力状态下的等效应力与等效应变的换算公式以及强度和寿命设计的安全系数.应用这些设计判据和安全系数,进行汽轮机零部件的强度设计和寿命预测,为汽轮机零部件的长周期安全运行提供了依据.     

金沙江向家坝水电站坝基砂岩蠕变特性研究

选取了金沙江向家坝水电站坝基的典型砂岩试样,采用三轴压缩试验对砂岩蠕变特性进行研究,分析了流变失稳破坏时的特征及砂岩的轴向、侧向和体积应变的全过程蠕变曲线异同点,对砂岩的长期强度进行预测分析。试验结果表明,砂岩存在一个起始蠕变应力阈值,每级荷载下的蠕变曲线之前都存在一个瞬时应变且随着围压的增大和偏应力的增大幅度越来越小,轴向瞬时应变与偏应力具有很好的线性关系;侧向和体积变形则存在明显的蠕变三阶段,加速阶段要比轴向快且两者的蠕变曲线形状相似,在同一围压和同一级偏应力下侧向蠕变量比轴向及体积的大,其蠕变发展最快;砂岩的长期强度可用等时偏应力应变曲线簇来进行确定,采用体积偏应力应变曲线簇更适宜,在已有的流变模型中伯格斯模型能较好的反映砂岩蠕变特性。     

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.