Computational study of CO2 methanation over two-dimensional molybdenum carbide catalysts

Two-dimensional molybdenum carbide (2D-Mo₂C) is thought to be promising for catalytic hydrogenation of CO₂ to CH₄, but little is known about its catalytic reaction mechanism. In this work, we investigate the hydrogenation of CO₂ to CH₄ on 2D-Mo₂C using density functional theory. Our calculations show that Mo on the surface can efficiently decompose CO₂ to CO and O, and also H₂ to H. The hydrogenation of CO produces CHO that is readily deoxygenated to CH, and CH is selectively hydrogenated to produce CH₄. Interestingly, the embedded Ir₁ on 2D-Mo₂C can act as a single-atom promoter to improve the performance of CO₂ methanation, while on the other hand maintaining its high selectivity for CH₄. This work provides insight into the mechanism of 2D-Mo₂C-catalyzed CO₂ methanation reactions and suggests a strategy to improve the performance of such catalysts through single-atom promoters.     

The drillstring dynamic frequency domains modes and mode shapes characteristics of compound drilling for the high-quality slim borehole

High-quality borehole is crucial to hydrogen underground storage (HUS) and oil & gas development, while compound drilling plays an important role in improving borehole quality. The modal model of compound drillstring in slim borehole is established by using finite element method to analyze the modal of longitudinal vibration, lateral vibration and torsional vibration. The results shows that as the number of order increases, the intrinsic frequency of the three vibrations increases. The amplitude of axial vibration is the largest, and the amplitude of lateral vibration is smallest. The natural frequency of drillstring in slim borehole decreases as drillstring length increasing. The longer drillstring is, the smaller the interval frequency between the intrinsic frequencies of orders will be, and it is easier to cause resonance. The axial vibration will cause minimal damage to the HUS quality. Lateral vibration has the greatest damage to wellbore quality, and is the most unfavorable for the establishment of HUS channels. The damage of torsional vibration to the HUS is less than the lateral vibration and larger than axial vibration. The higher the vibration frequency and amplitude, the harder it is to improve the HUS quality. In order to improve the quality of HUS, the weight on bit (WOB) and rotary per minutes (RPM) should be adjusted at the same time for lateral shock, and the WOB should be mainly reduced for controlling the axial and torsional vibration. The results are benefit for the drillstring design, improving the wellbore quality and HUS quality.     

Study on the role of niobium in corrosion mechanism of low-alloy pipeline steel in H2S-saturated solution

In this study, the role of Nb addition on the corrosion behavior of low-alloy steel exposed to H₂S solution is studied by means of microstructure, macro/microsurface morphology characteristics, type of corrosion product, cross-sectional structure and elemental distribution. The addition of Nb is a route to refine grains and improve corrosion resistance. The surface formation process of iron sulfides changes from homogeneity to dispersion at the initial corrosion stage when Nb is added to steel. However, the transformation process and crystal structure of iron sulfides are not affected by the addition of Nb. The elemental distribution of corrosion products is not affected by Nb addition although thick and compact corrosion products are formed on the specimen surface of Nb steel. A schematic model is proposed to clarify the difference of the corrosion mechanism in atomic and molecular level.     

Electrochemical performance study of proton exchange membrane electrolyzer considering the effect of bubble coverage

Bubble dynamics are closely related to the electrochemical performance of a proton exchange membrane electrolyzer (PEMEC). However, tiny bubbles need to be clustered together to affect the electrochemical performance of PEMEC significantly. In this paper, the effect of microscopic bubbles on macroscopic electrochemical properties were assessed by bubble coverage. The bubble dynamics, two-phase flow, and electrochemical performance were captured under different conditions using a high-speed, microscopic visualization experimental system. The results show that various factors influence the two-phase flow pattern. At 60 °C, 1.5 A/cm² and 5 mL/min, the annular flow occupied 76.8% of the gas phase area, and when the water flow increased to 80 mL/min, the annular flow ratio decreased substantially to 2.7%. The two-phase flow of bubbles in the flow channel showed different flow patterns over time. Under the experimental conditions (60 °C, 20 mL/min, 0.8 A/cm²), the bubble flow pattern experienced the emergence of bubbles, bubble flow, segmental plug flow, annular flow, and final steady state with the occurrence times of 0.15 s, 1.5 s, 5.0 s, 10.5 s, and 21.2 s, respectively. The bubble coverage increased with current density and temperature, while it decreased with the increase of water velocity. In addition, the effects of temperature and water velocity on bubble coverage and PEMEC performance vary in principle. Specifically, higher temperature mainly improves the bubble coverage by increasing the electrochemical performance of PEMEC. In contrast, higher water velocity mainly improves the electrochemical performance of PEMEC by decreasing the bubble coverage. This study elucidates the relationship between microscopic bubbles and macroscopic electrochemical performance, contributing to a better understanding of the processes and principles of bubble effects on the electrochemical performance of PEMEC. The results may provide a theoretical basis and experimental data for operating condition optimization, operating efficiency improvement, multiphase flow study, gas diffusion layer structure, and flow field design of PEMEC.     

信息物理系统架构下集群风电自适应控制方法

针对传统集群风电有功控制模式中安全裕度偏于保守的问题,基于信息物理系统架构提出了一种面向集群风电的运行断面自适应控制方法.基于风电场功率响应特性,提出了断面裕度动态计算的实现方法.根据断面裕度动态计算结果和风电场的发电状态,动态调整风电场运行方式,实现集群风电与运行断面间的自适应.基于某地区电网实际数据构造的算例表明,所提出的方法在降低断面越限时间33. 3%的同时,能减少弃风约21. 4%.该方法对提升运行断面传输利用率、降低运行断面越限时间具有促进作用.     

NERC compliant load frequency control design using fuzzy rules

This paper presents a load frequency control design for interconnected electric power systems using a set of fuzzy logic rules. The design objectives are (i) to comply with the North American Electric Reliability Council's (NERC) control performance standards, CPS1 and CPS2, (ii) to reduce wear and tear of generating unit's equipments, and (iii) to design a feasible control structure. A test system with multiple generation and distribution companies that takes into account regulation and load following services is used to demonstrate the effectiveness of the proposed methodologies.     

高压换流站的主要电磁骚扰源特性

为研究换流站抗干扰设计基础的电磁骚扰源特性,采用基于EMTP的宽频时域电路方法和矩量法的频域电磁场计算方法分析了换流阀导通和关断时产生的骚扰水平,试验研究了断路器操作引起的电磁骚扰特性。研究结果表明,传导骚扰可覆盖达数MHz的频率范围,辐射骚扰在数MHz附近问题最严重,该类电磁噪声是直流高压换流站中最重要的骚扰源;直流系统操作会在二次电缆中产生几百V的振荡衰减波,直流管母线起晕电压高,直流场电晕引起的无线电骚扰水平较低。     

NOSA五星安健环管理系统在发电企业的综合应用

介绍了国际职业安全协会（NOSA）五星安全、健康、环境保护综合风险管理系统及危险源辨识、风险评价的基本概念,重点论述了三者间的关系,结合发电企业的实例,提出了将三者融为一体实现闭环管理,进而有效推行NOSA五星安全、健康、环境保护综合风险管理系统,最终促使企业形成自我改进、不断完善的安全管理机制的新思路。     

Integrated smart grid systems security threat model

The smart grid (SG) integrates the power grid and the Information and Communication Technology (ICT) with the aim of achieving more reliable and safe power transmission and distribution to the customers. Integrating the power grid with the ICT exposes the SG to systems security threats and vulnerabilities that could be compromised by malicious users and attackers. This paper presents a SG systems threats analysis and integrated SG Systems Security Threat Model (SSTM). The reference architecture of the SG, with its components and communication interfaces used to exchange the energy-related information, is integrated with the results of SG systems security threat analysis to produce a comprehensive, integrated SG SSTM. The SG SSTM in this paper helps better depict and understand the vulnerabilities exploited by attackers to compromise the components and communication links of the SG. The SG SSTM provides a reference of the systems security threats for industrial security practitioners, and can be used for design and implementation of SG systems security controls and countermeasures.     

Enhancing the microstructure and tensile creep resistance of Sn-3.0Ag-0.5Cu solder alloy by reinforcing nano-sized ZnO particles

Sn-Ag-Cu lead-free solders are regarded as a potential substitute for Pb-Sn solder alloys. In the current study, the non-reacting, non-coarsening ZnO nano-particles (ZnO NPs) were successfully incorporated into Sn–3.0Ag–0.5Cu (SAC305) lead-free solder by mechanical mixing of ZnO powders and melting at 900 °C for 2 h. Tensile creep testing was performed for plain SAC305 solder and SAC305-0.7 wt% ZnO NPs composite solders and a Garofalo hyperbolic sine power-law relationship was created from the experimental data to predict the creep mechanism as a function of tensile stress and temperature. Based on the tensile creep results, the creep resistance of SAC305 solder alloy was improved considerably with ZnO NPs addition, although the creep lifetime was increased. From microstructure observation, reinforcing ZnO NPs into SAC305 solder substantially suppressed the enlargement of Ag₃Sn and Cu₆Sn₅ intermetallic compound (IMC) particles and decreased the spacing of the inter-particles between them, reduced the grain size of β-Sn and increased the eutectic area in the alloy matrix. The modification of microstructure, which leaded to a strong adsorption effect and high surface-free energy of ZnO NPs, could result in hindering the dislocation slipping, and thus provides standard dispersion strengthening mechanism. Moreover, the average activation energy (Q) for SAC305 and SAC305-0.7ZnO alloys were 50.5 and 53.1 kJ/mol, respectively, close to that of pipe diffusion mechanism in matrix Sn.