考虑导叶分段关闭特性的水轮机调速系统改进模型

针对电力系统分析软件PSD-BPA中水轮机调速系统的执行机构模型不能有效反映实际特征且混流式水轮机模型仿真精度不高的问题,提出了考虑导叶分段关闭特性的执行机构模型,设置不同的分段点对机组甩负荷进行了仿真分析,并对计及功率与开度间非线性关系的混流式水轮机解析非线性模型进行研究。仿真及实测分析结果表明,考虑导叶分段关闭特性的水轮机调速系统改进模型能准确仿真混流式水轮机组导叶分段关闭规律,比BPA模型的开度及功率响应更切合实际,更能体现其有效性。     

计及功率与导叶开度非线性特性的混流式水轮机改进模型

针对现有理想水轮机模型和解析非线性水轮机模型不能反映混流式水轮机组功率与导叶开度间的非线性特性问题,建立了计及功率与开度非线性特性的混流式水轮机改进模型。该模型基于水轮机解析非线性模型,加入了功率与开度非线性关系模块,分析比较了功率与开度的不同拟合方法,推荐采用三次多项式拟合方法更适用于功率与开度拟合,并通过机组频率扰动试验、功率升降试验、一次调频试验和电网故障扰动试验仿真及实测结果表明,与理想水轮机模型和解析非线性水轮机模型相比,计及功率与开度非线性特性的水轮机改进模型精度更高。     

导叶不同开度下抽水蓄能机组水轮机工况内流特性分析

为了解抽蓄机组水轮机工况下活动导叶不同开度下的内流特性,以某抽水蓄能电站水泵水轮机为研究对象,基于SST k-ω湍流模型,进行活动导叶不同开度下全流道三维非定常数值模拟和分析,探讨活动导叶开度对过流部件内部流场的影响.结果表明:随着导叶开度的增加,水泵水轮机的流量增大,转轮力矩增大但增幅降低,效率先增大后降低.蜗壳整体上的压力沿周向分布比较均匀,从蜗壳进口到蜗壳出口均匀降低,水力损失较小;固定导叶形状及安放角与活动导叶搭配影响较大,小开度和大开度工况下活动导叶和固定导叶进口处水力损失大;压力变化线与进出口是否平行影响转轮内部流态,中开度转轮叶片做功最好;小开度工况下易产生偏心涡带,降低机组效率,不利于尾水管能量的回收,中开度工况下尾水管流态最好.研究结论对抽水蓄能机组运行提供了理论参考.     

导叶开度对混流式水轮机尾水管内流动特性的影响

为了深入研究尾水管内的流动特性,结合某电站混流式水轮机的实际运行情况,基于标准的κ-ε湍流模型,选用Fluent软件在额定水头不同导叶开度下对其进行全流道数值模拟,分析了不同导叶开度对混流式水轮机尾水管内部流动特性的影响。结果表明,当导叶开度为100%时尾水管内部形成了周期空化涡带,此涡带的存在易导致水轮机机组产生强烈振动;当导叶开度较小时,尾水管内速度分布较为均匀;尾水管进口段的压力分布情况对导叶开度的变化较为敏感,可通过合理控制导叶开度来减小尾水管内的水力振动,降低水力损失。     

基于改进粒子群算法的水轮机调速系统建模

针对电力系统稳定计算分析软件中水轮机调速系统模型过于简单、粗略的问题,建立了水轮机调速系统非线性模型,并提出参数实测与改进的粒子群智能优化算法结合的模型辨识方法,获得了调速器模型参数、水轮机-引水道模型参数.现场实测数据的模型仿真结果验证了该模型辨识方法的准确性,该模型优于电力系统稳定计算软件中的模型,更符合实际.     

叶片开度对贯流式水轮机飞逸过程的影响

为有效降低水轮机飞逸过程中机组的振动问题,通过水轮机试验模型改变导叶开度和桨叶开度对水轮机过渡过程进行研究,分析了多个监测点的压力、频率流量等工作参数的变化情况.结果 表明,由于转速和流量的增加,水轮机在导叶开度60°和桨叶开度4°运行时振动最为强烈,水轮机在低频时振动剧烈.由于受到导叶和桨叶动静影响,转轮出口振动强烈...     

基于水轮机导叶转角推求导叶开度圆直径的方法

鉴于反击式水轮机活动导叶开度大多采用导叶转角描述,而在水电工程初步设计阶段开展的相关设计计算工作中,仍采用导叶开度圆直径描述现状,以活动导叶数为24只的圆柱式导水机构为基础,提出了水轮机导叶转角与导叶开度圆直径之间的转换公式。同时,通过对一系列典型导叶布置图的分析,结合数值分析方法,对公式中的修正系数给出了明确的解析表达式,并验证了表达式的可靠性。     

超低水头轴流式水轮机CFD优化及流动特性研究

结合某水电站改造要求,研发了一种设计水头为2.75 m的超低水头轴流式水轮机并对其性能进行优化,以达到有效利用低水头水力资源的目的。基于不可压缩连续方程及雷诺时均Navier-Stokes方程,采用Spalart-Allmaras湍流模型和SIMPLEC算法对轴流式水轮机进行三维全流场数值模拟,分别分析了轴流式转轮叶片翼型、轮毂比、导叶开度及安放角对水轮机性能的影响,并对最优模型进行实测验证。结果表明,在满足设计水头为2.75 m的情况下,选用配置叶片B、轮毂比为0.30、叶片相对安放角为-2°的水轮机,当导叶相对开度为0°时,装置水力损失最小,最高效率达83.7%,且数值模拟计算所得出力与实测结果误差小于099%,表明基于CFD的数值模拟对超低水头轴流式水轮机的性能预测精度较高。     

水泵水轮机四象限工况无叶区内流场PIV试验研究

鉴于PIV(粒子图像速度仪)是对流体机械内部流场进行试验研究的重要技术,以某模型水泵水轮机为例,设计搭建了模型试验台,并对试验部件进行可视化处理,利用PIV测试了水泵水轮机无叶区的四象限工况(8个开度)的内部流场,并对无叶区的速度内流分布经过PIVView3C后处理得到流线图和速度分布图。结果表明,最优开度的流线图优于导叶开度20°的内流流态,导叶开度20°的内流流态相比导叶开度5°较好,导叶开度5°的漩涡更加密集;导叶开度5°工况下的流场具有周期性变化趋势,是造成无叶区产生压力脉动的主要原因。     

小弦节比贯流水轮机On-Cam开度设计

针对贯流式水轮机活动导叶与转轮叶片均为可动翼,为确保水轮机高效率运行,对构不成流路通道、不适用流道理论的小弦节比贯流式水轮机3叶片转轮进行协联工况预测,提出了翼型设计后采用CFD数值模拟预测协联组合开度法.实例验证了该法的可行性,并可确定导叶开度与转轮叶片开度的最优组合(On-Cam)开度.     

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%.     

Contents in Volume 23,2014

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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.     

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.