我国火电厂自动化与信息化技术的进展

围绕近年来我国火电厂的分散控制系统、可编程序控制器、厂级监控系统、现场总线控制系统、快速甩负荷、辅机故障减负荷、火电机组一键启停、燃烧优化控制、机组诊断、容错保护和优化汽温控制等技术的应用,阐述了我国在控制系统硬件和监控系统应用软件等方面取得的成果,指出火电厂自动化和信息化今后的重点发展任务是继续深入研究、完善并发展自动化和信息化技术用于火电厂生产过程,配合超临界大型发电机组和新型发电技术的应用,以保证火电厂的经济效益和可靠运行.     

具有整体围带和凸台拉筋汽轮机长叶片阻尼振动特性实验研究

阻尼围带和凸台拉筋结构在大型汽轮机叶片中被广泛采用来增加叶片阻尼,降低其振动应力.设计并建造了阻尼结构叶片振动特性实验台,对一具有阻尼围带和凸台拉筋汽轮机长叶片的阻尼器接触面施加不同转速下的正压力进行了振动特性测试,得到了不同转速正压力下叶片的频响曲线和模态阻尼比.试验结果表明:只有围带接触时,随着转速的增加,叶片模态阻尼比先增后减;围带和拉筋都接触时,也存在同样的现象.当转速大于2 600r/min后,叶片的共振频率基本不变且模态阻尼比与自由叶片时基本一致.     

高温下氧气氛对煤焦还原NO影响机理研究

利用高温刚玉管固定床反应器,研究了恒温条件下氧气氛对2种动力煤煤焦与NO异相还原反应的影响规律,以此探讨高温下氧气氛对煤焦还原NO行为的影响机理.实验结果表明,在高温条件下,氧气浓度对C-NO反应的影响也存在临界值,且与低温试验相比,在更低氧浓度时即达到临界值.氧浓度对高挥发分、低灰的煤焦样品的影响作用较为明显;同时,...     

Experimental investigation on heat transfer characteristics of low mass flux rifled tube with upward flow

An experiment for heat transfer of water flowing in a vertical rifled tube was conducted at subcritical and supercritical pressure. The main purpose is to explore the heat transfer characteristics of the new-type rifled tube at low mass flux. Operating conditions included pressures of 12–30 MPa, mass flux of 232–1200 kg/(m² s), and wall heat fluxes of 133–719 kW/m². The heat transfer performance and wall temperature distribution at various operating conditions were captured in the experiment. In the present paper, the heat transfer mechanism of the rifled tube was analyzed, the effects of pressure, wall heat flux and mass flux on heat transfer were discussed, and corresponding empirical correlations were also presented. The experimental results exhibit that the rifled tube has an obvious enhancement in heat transfer, even at low mass flux. In comparison with a smooth tube, the rifled tube efficiently prevents Departure from Nucleate Boiling (DNB) and delays dryout at subcritical pressure, and also improves the heat transfer of supercritical water remarkably, especially near pseudo-critical point. An increase in pressure or wall heat flux impairs the heat transfer at both subcritical and supercritical pressure, whereas the increasing mass flux has a contrary effect.     

Direct simulation of turbulent heat transfer in swept flow over a wire in a channel

We investigate heat transfer characteristics of a turbulent swept flow in a channel with a wire placed over one of its walls using direct numerical simulation. This geometry is a model of the flow through the wire-wrapped fuel pins, the heat exchanger, typical of many civil nuclear reactor designs. The swept flow configuration generates a recirculation bubble with net mean axial flow. A constant inward heat flux from the walls of the channel is applied. A key aspect of this flow is the presence of a high temperature region at the contact line between the wire and the channel wall, due to thermal confinement (stagnation). We analyze the variation of the temperature in the recirculation bubble at Reynolds number based on the bulk velocity along the wire-axis direction and the channel half height of 5400. Four cases are simulated with different flowrates transverse to the wire-axis direction. This configuration is topologically similar to backward-facing steps or slots with swept flow, except that the dominant flow is along the obstacle axis in the present study and the crossflow is smaller than the axial flow, i.e., the sweep angle is large. The temperature field is simulated at three different Prandtl numbers: 10^?2, 10^?1 and 1. The lower value of Prandtl number is characteristic of experimental high-temperature reactors that use a molten salt as coolant while the high value is typical of gas (or water vapor) heat exchangers. In addition, mean temperature, turbulence statistics, instantaneous wall temperature distribution and Nusselt number variation are investigated. The peak Nusselt number occurs close to the reattachment location, on the lee side of the wire, and is about 50–60% higher compared to the case without crossflow. The high temperature region follows the growth of the recirculation bubble which increases by about 65% from the lowest to highest amount of crossflow. Particular attention is devoted to the temperature distribution on the walls of the channel and the surface of the wire. The behavior of the heat-flux across the mean dividing streamline of the recirculation bubble is investigated to quantify the local heat transfer rates occurring in this region.     

钙基吸收剂循环吸收CO2特性的研究进展

采用钙基吸收剂循环吸收CO2是目前理论比较成熟,前景比较好的零排放技术。通过对钙基吸收剂吸收CO2现状技术和改善其吸收特性方法的总结,探讨了钙基吸收剂的选择、吸收CO2的效率、循环吸收效率下降的原因和循环流化床吸收CO2系统,为CO2的捕集和吸收提供了有益参考,同时提出了以后研究需要改进的内容,为后期的实验研究指明了方向。     

660MW超超临界汽轮机能级效率计算分析

通过采用能级效率法对660 MW超超临界汽轮机热力系统的VWO、TMCR、THA、75％ THA、50％ THA等工况进行了能损分析,获得了各工况下热力系统的各能级效率、各辅汽水和纯热力的能损值,从而验证了能级效率法的精度和易用性,并获得了降低汽动给水泵小汽机用汽的能级是进一步降低660 MW超超临界汽轮机热力系统能损的有效途径.     

褐煤干燥提质技术比较与水分回收及余热利用方案

针对褐煤的高水分、低热值、易风化自燃、难以洗选、储存和运输等缺点,总结研究目前褐煤干燥脱水技术,并提出一套针对燃煤电站的褐煤干燥及其高水分烟气水分回收与余热来利用的方案,从而提高褐煤使用范围和经济性以适应当前能源紧缺及节能环保的能源局面。     

高压直流线路开路试验的控制原理及保护分析

高压直流线路开路试验是一种检测手段,主要是对换流站直流侧进行加压,其控制理念和相关保护全然不同。若控制保护异常,直流电压会异常升高或者不变,最终导致试验失败。结合常规直流系统线路开路试验,介绍了线路开路试验的控制原理,比较了理论计算与实际工程中的母线电压最大值,得出直流线路电压参考值和实际电压测量值可以同步变化,差值不超过10kV。为了在试验不成功时闭锁换流器,采用了ABB公司Mach2系统中的电压差值保护、过流保护、过流后备保护和保护性触发等保护技术。通过保护分析得出:在原理上、工程上、保护上,直流系统的正常运行和开路试验有所不同。     

A reaction mechanism for gasoline surrogate fuels for large polycyclic aromatic hydrocarbons

This work aims to develop a reaction mechanism for gasoline surrogate fuels (n-heptane, iso-octane and toluene) with an emphasis on the formation of large polycyclic aromatic hydrocarbons (PAHs). Starting from an existing base mechanism for gasoline surrogate fuels with the largest chemical species being pyrene (C₁₆H₁₀), this new mechanism is generated by adding PAH sub-mechanisms to account for the formation and growth of PAHs up to coronene (C₂₄H₁₂). The density functional theory (DFT) and the transition state theory (TST) have been adopted to evaluate the rate constants for several PAH reactions. The mechanism is validated in the premixed laminar flames of n-heptane, iso-octane, benzene and ethylene. The characteristics of PAH formation in the counterflow diffusion flames of iso-octane/toluene and n-heptane/toluene mixtures have also been tested for both the soot formation and soot formation/oxidation flame conditions. The predictions of the concentrations of large PAHs in the premixed flames having available experimental data are significantly improved with the new mechanism as compared to the base mechanism. The major pathways for the formation of large PAHs are identified. The test of the counterflow diffusion flames successfully predicts the PAH behavior exhibiting a synergistic effect observed experimentally for the mixture fuels, irrespective of the type of flame (soot formation flame or soot formation/oxidation flame). The reactions that lead to this synergistic effect in PAH formation are identified through the rate-of-production analysis.