Assessment of technical and economic efficiency of a closed hydrogen cycle at NPP

The paper deals with the technical and economic efficiency of combining NPP with the hydrogen energy complex (HEC) based on a closed hydrogen cycle. At the present stage of studying, the use of hydrogen produced through electrolysis (electrolysis hydrogen, EH) is a well-known approach to providing NPP with a base load during hours of minimum electrical load in the energy system (ES). Despite the existing concerns about the safety of using hydrogen fuel in the cycles of thermal power plants (TPP), this approach could improve NPP efficiency by accumulating the unused night-time electricity succeeded by generation of additional electricity during the hours of maximum electrical loads in ES. This provides further development of clean energy on the basis of atomic-hydrogen technologies. In the paper, the technical and economic efficiency of implementing the closed hydrogen cycle at NPP depending on the cost of the off-peak electricity required for HEC has been investigated.The assessment of the main technical and economic efficiency indicators of the basic equipment for HEC based on a closed hydrogen cycle preventing hydrogen from penetrating into the main steam cycle has allowed analyzing the efficiency of combining NPP with HEC. For this purpose, an increase of the steam-turbine unit (STU) capacity due to an increase in steam consumption along with the flowing section efficiency has been estimated; the required heat exchanging area for a closed system of hydrogen steam superheating (HSS) has been determined on the basis of the heat and mass transfer process calculations; and capital expenditures (CAPEX) as well as operating expenses (OPEX) have been calculated. As an example, a comparative assessment of two alternative methods for implementing a closed hydrogen cycle has been performed: at elevated and atmospheric pressure of combustion products.The calculation results have allowed determining key figures of comparative technical and economic efficiency of implementing the proposed schemes for combining NPP with HEC based on a closed hydrogen cycle. Zones of economic efficiency depending on the cost of off-peak electricity for the needs of the hydrogen energy complex have been determined as well. The calculations have shown that reducing the pressure of combustion products to the atmospheric one may result in a certain decrease in the efficiency of the closed hydrogen cycle. These results could be used in developing and optimizing the systems for increasing an economically sound maneuverability of NPP based on combining with HEC.     

金属纳米晶体熔化与过热的等效模型

从Hill微系统热力学理论出发,根据已建立的金属纳米晶体结合能的等效模型与相应熔化热力学模型,建立了简单、实用的金属纳米晶体熔化与过热的等效模型．模型不仅预测了随表面原子百分数的增大自由表面纳米晶体熔点与熔化熵的减少及包覆纳米晶体熔点与熔化熵的增加,还对纳米晶体产生过冷和过热的条件进行了分析．对金属纳米微粒、纳米线及纳米薄膜的熔点、熔化熵增大或减少的预测值与实验结果相一致．     

一段炉过热蒸汽低温盘管损坏情况分析

介绍过热蒸汽管线工艺改进方法及一段转化炉对流段过热蒸汽低温盘管损坏经过和原因,提出设备修复方法。     

W型火焰锅炉动态特性的数值计算与研究

对Ｗ型火焰锅炉的蒸发系统、过热器系统的动态特性进行了数值计算与研究。详细分析了上安电厂Ｗ型火焰锅炉在不同负荷、不同运行方式、不同卫燃带面积等条件下的蒸发特性及汽温特性的动态变化过程,论述了其变负荷性能差的主要原因。计算数据反映的规律符合实际运行情况。     

Influence of melt superheating on microstructures of Mg-3.5Si-1 Al alloys

The influence of melt superheating treatment on the microstructures of Mg-3.5Si-1Al alloys unmodified and modified with 0.2%Sr-Sb(mass fraction) was investigated.The results show that when the melt superheating temperature increases from 750 to 900℃,the average size of primary Mg2Si in the unmodified alloys decreases progressively from about 27 to about 19μm,while that in Sr-Sb-modified alloys is refined considerably from about 14 to about 7μm when the temperature increases from 750 to 850℃,and then slig...     

Effect of melt superheating treatment on crystallization behavior and magnetic properties of melt-spun Fe-rich Nd-Fe-B ribbons

Melt-spun Nd7Fe90B3 ribbons were prepared under different melt treatment conditions,i.e.,the melt temperature was varied prior to ejection onto the quenching wheel.The microstructure characteristics,crystallization behavior,and subsequent magnetic properties of α-Fe/Nd2Fe14B-based exchange-spring magnets were investigated using X-ray diffraction,differential scanning calorimeter,transmission electron microscopy,and vibrating sample magnetometer.It was shown that melt spinning at different quenching temperat...     

On the Critical Point of Tungsten

Experimental results of exploding tungsten wire experiments with heating rates of 10¹⁰ to 10¹¹ Ks^–1 are interpreted using a one-dimensional hydrodynamic model. The vaporization dynamics under these conditions are discussed. It is shown that for the wires used the superheating of the liquid phase is small and vaporization starts close to the binodal line of the phase diagram. Due to inertia, a volume vaporization takes place in a thin surface layer, while in the bulk of the column formed by the exploding wire a pressure of the order of 10 kbar is maintained. Sufficiently uniform density and temperature distributions are formed in the liquid core surrounded by the two-phase layer. This behavior of vaporizing wires was used to obtain the thermal expansion coefficient of liquid tungsten along with its critical point parameters.     

Superheating and melting behaviors of Ag clusters with Ni coating studied by molecular dynamics and experiments

Using molecular dynamics with embedded-atom-type interatomic potentials, we simulated the melting behavior of a spherical Ag3055 cluster coated with Ni. The semi-coherent Ag/Ni interface formed at low temperatures acts as an effective barrier against the surface melting and leads to a substantial superheating of the Ag cluster. The melting point was found to be about 100 K above the equilibrium melting point of the bulk Ag crystal (1230 K?15 K) and about 290 K above that (1040 K) of the free Ag3055 cluster. A superheating of 70 K was observed in the high-temperature differential scanning calorimetry measurement for Ag particles with a mean size of 30 nm embedded in Ni matrix prepared by means of melt-spinning. Melting is initiated locally at the defective interfacial area and then propagates inwards, suggesting a heterogeneously nucleated melting event at the Ag/Ni interface.     

Transient Boiling of Sodium in Seven-Pin Bundle under Transient Overpower Conditions

Transient sodium boiling experiments were conducted in an electrically heated 7-pin bundle under transient overpower conditions. In each run the heater power was gradually raised at almost constant rate under forced convection.

The observed coolant voiding was initially limited to the central subchannel on account of an appreciable time lag in temperature rise occurring between the central and peripheral subchannels. This would appear to call for calculations with two-dimensional voiding model.

The bulk pressure rises registered upon initial vaporization were markedly lower than the vapor pressure corresponding to the incipient-boiling (IB) wall superheat. The pressure pulse generated upon vapor bubble collapse correlated reasonably well with the re-entrant liquid velocity, but the measured value was very much smaller than predicted theoretically from sodium hammer analysis.     

Effect of Melt Superheating Treatment on Directional Solidification Interface Morphology of Multi-component Alloy

The influence of melt superheating treatment on the solid/liquid (S/L) interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity (R) but also to the melt superheating temperature (Ts) when the thermal gradient of solidification interface remains constant for different Ts with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when Ts increases from 1500°C to 1650°C, and maintains plane with further elevated Ts of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when Ts increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when Ts increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.