板坯连铸动态二冷配水技术的工业应用

基于耦合多元合金两相区凝固模型的板坯连铸凝固传热数学模型和恒间距切片单元跟踪方法,开发了板坯连铸动态二冷配水软件平台,其中内嵌二冷分区有效拉速和目标表面温度曲线两种控制模式,前者充分考虑了铸坯的冷却历史,后者则关注对铸坯表面温度沿铸流方向的合理控制,在实际生产中可以方便灵活地加以选择应用.该技术控制功能丰富、安全机制完...     

小方坯帘线钢末搅参数的优化研究

以小方坯帘线钢的连铸生产为研究对象,采用ProCast商业软件根据实际生产的工艺参数建立铸坯的凝固传热模型,并利用射钉试验对模型进行校正以提高模型的准确性。结果表明,该凝固传热模型可以模拟帘线钢的连铸生产过程。根据射钉试验和数值模拟结果,对末搅位置进行改进,可发现铸坯中心缩孔等级下降,等轴晶率增大。     

热送热装工艺中板坯出连铸机温度的分折

用连铸坯凝固过程传热模型模拟了热送热装工艺中不同工况下铸坯凝固壳厚度和铸坯出连铸机的温度变化。模拟结果与实测值吻合很好。影响铸坯出连铸机温度的主要因素是铸坯尺寸、连铸机拉迪和冷却制度。适当提高拉速及改善连铸机二冷区冷却制度有利于高温铸坯的生产。     

高碳耐磨球钢大方坯连铸过程凝固性能的仿真分析

应用有限元分析软件建立290 mm×380 mm大方坯连铸过程凝固传热模型,模拟不同碳质量分数高碳耐磨球钢大方坯宽面和窄面凝固坯壳的生长规律。研究结果表明:该模型通过计算得到铸坯宽面的外壳温度还有铸坯宽面、窄面中心的凝固坯壳厚度进行对比分析,验证了该数学模型可以表达凝固坯壳厚度的分布情况,最终达到准确推测凝固终点位置的目的。在弯月面到二冷出口这一阶段,凝固时间和凝固坯壳厚度d显示出线性关系。在距弯月面10 m到凝固终点这一阶段,凝固时间t1/2和坯壳厚度d并不是线性关系,且铸坯中心等轴晶区域出现。     

中间包两相流场的数值模拟和操作优化

为了提高20#碳钢连铸管坯的产品质量，通过对气泡和非金属夹渣的形成机理以及对中间包内钢水流场数值模拟的研究分析，发现中间包的结构与操作对20#钢连铸坯的生产质量具有较大影响，因此，对中间包的结构与操作进行了优化研究，研究结果显示：(1)通过对中间包的结构优化提高了中间包的钢水液面高度，增加了钢水在中间包内的滞留时间，有利于夹杂物和气泡的消除，从而提高了钢水的均匀性；(2)改进钢水流入、流出中间包的操作，能避免钢流与空气的直接接触，减少钢水的二次氧化；(3)连铸钢水过热度的严格控制，有利于减少钢水的二次氧化和对包衬耐火材料的浸蚀，从而起到降低铸坯中非金属夹渣物的效果。采取这些措施后，2#钢连铸坯的质量取得了显著提高，设备寿命明显延长。     

热送热装工艺中板坯出连铸机温度的分析

用连铸坯凝固过程传热模型模拟了热送热装工艺中不同工况下铸坯凝固壳厚度和铸坏出连铸机的温度变化。模拟结果与实测值吻合很好。影响铸坯出连铸机温度的主要因素是铸坯尺寸、连铸机拉速和冷却制度。     

45#钢连铸坯凝固过程数值模拟与验证

根据实际生产的工艺参数,通过ProCAST商业软件对45#钢连铸坯的坯壳厚度以及凝固过程进行数值模拟,并进行现场射钉实验对模拟结果验证。结果表明,数值模拟与现场二级模型相比其结果更接近于射钉实验所得坯壳厚度,说明数值模拟相对于现场二级模型更能有效地反映出铸坯不同位置坯壳厚度,为末端电磁搅拌提供有效的参考。     

特殊钢生产技术的发展及对内燃机零件用钢选择的思考

机电产品大量使用各种特殊钢。随着特殊钢的冶炼、铸坯、成型技术发展,不同铸坯方式的结晶学特征以及最终材料的质量,发生了显著的变化。对铸锭-开坯-轧(锻)制成材与连铸连轧成材的工艺特点和钢材的质量进行比较,对钢材的选择提出一些应考虑的问题。     

连铸二次冷却控制技术的发展

通过对连铸二冷控制技术的归类,简述了拉速关联配水、基于传热模型在线计算动态控制、基于传感器测温反馈控制、基于有效拉速计算动态控制、人工智能优化控制5大类控制方式的控制理念及特点,在连铸设计及生产中,提出了各类二次冷却控制方式可根据生产实际需要进行选择的建议.合理的二次冷却控制方式对于确保铸坯质量有着重要意义.     

攀钢板坯连铸二冷喷嘴性能的热态实验研究

基于钢坯的非稳态导热原理,采用金属试样单侧加热至二冷段金属表面温度再进行冷却的实验方法,模拟水/气-水喷嘴性能对钢坯冷却过程的影响.按攀钢板坯连铸的二冷段喷嘴布置方式和主要生产铸坯的品种规格,设计喷嘴特性与单、双喷嘴条件下铸坯强制冷却传热过程研究的实验方案.通过对喷嘴传热性能的测试,得到了水/气-水喷嘴在不同喷水压力下的传热系数;实验得到的双喷嘴平均传热系数与生产过程数据计算的传热系数的误差在5%～9%以内,研究结果表明喷嘴传热性能的热态实验可以为合理布置喷嘴、优化二冷制度提供依据.     

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%.     

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.     

Contents in Volume 23,2014

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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.