Increasing profit by improving gas handling systems

The availability of a smelter’s gas handling systems is crucial to the profitability of the plant. In new projects, the best technical and economic result is achieved if the gas handling systems are integrated into the process. This integration requires close cooperation between the smelter process designer and the gas handling designer. In modernization projects, environmentally, economically, and technically feasible solutions can be found, and smelter productivity can be increased when imagination and new technology are applied.     

Interaction of particles with carrier gas in HVOF spraying systems

Several designs of high-velocity oxygen fuel (HVOF) thermal spray systems have been created during the last decade. The most advanced systems are now producing coatings comparable in quality to detonation (D-gun) coatings. This paper presents numerical analysis of the interaction of dispersive particles with the carrying gas flow for three different HVOF systems, along with a method to calculate the parameters of sprayed particles that highlights the advantages and limitations of each design. The method includes gas dynamical calculations of the gas flow in an accelerating channel and calculations of the injected par-motion and thermal state (temperature and melted mass fraction). The calculations were performed for particles of tungsten carbide, aluminum oxide, and zirconium oxide with size distributions of 10 to 80 μm. Two conventional types of HVOF systems were considered: those with a supersonic accelerating channel and those with a subsonic accelerating channel (without a de Laval nozzle). A novel design is pro-posed that contains a combined gas dynamical path with functionally separated regions of heating and acceleration. The regularities and distinctions in the behavior of the metallic and ceramic oxide particles are discussed for different jet configurations. The results obtained indicate that it is possible to signifi-cantly affect particle parameters by using the new configuration solutions without creating construction complications.     

Investigation of systems for gas vortex stabilization of plasma torches

Several designs of plasma torches for cutting of metals are used to analyse the effect of design special features of the gas-air circuit on the efficiency of operation of the gas vortex stabilisation system. It is shown that the distribution of the flows of the plasma-forming gas in the cross section of the circuit is non-uniform. A method of stabilization by changing the dimensions of the expansion chamber is analysed. The main directions for further studies are outlined.     

Mathematical modeling of the gas and powder flow in HVOF systems

A mathematical model was developed to describe the gas dynamics and heat-transfer mechanism in the gas/particle flow of high- velocity oxyfuel (HVOF) systems. A numerical solution was carried out using a PC- based computer program. One- dimensional predictions of the temperature and velocity profiles of gas and particles along the axis of flow were obtained to conduct cost- effective parametric studies and quality optimization of thermal spray coatings produced by HVOF systems. The numerical computer model allows for the variation of the HVOF system parameters, such as air/fuel ratio and flow rates, cooling water inlet temperature and flow rate, barrel length, standoff distance, particle size, and gun geometry. Because of the negligible volume of the powder relative to the gas, the gaseous phase was modeled as continuous nonadiabatic, and friction flow with variable specific heats and changing cross- sectional areas of flow. The generalized continuity, momentum, and energy equations with the influence parameters were used to model the gaseous flow regime and predict its thermodynamic properties. Empirical formulas for the mean axial decay of both velocity and temperature in the supersonic jet plume region were generated from published measurements of these parameters using laser Doppler velocimeter and Ray leigh scattering techniques, respectively. The particle drag and heat- transfer coefficients were calculated by empirical formulas in terms of Reynolds, Nusselt, and Prandtl numbers to evaluate both the momentum and heat transferred between the combustion gases and the powder particles. The model predictions showed good agreement with the particle and gas temperature and velocity measurements that are available in the literature.     

The development of new bond coat compositions for thermal barrier coating systems operating under industrial gas turbine conditions

Environmental and economic issues are driving the development of increasingly efficient gas turbines. An important step in achieving this is to engineer components which can operate with longer lifetimes and at higher metal temperatures. Inlet temperatures for gas turbines now exceed the melting temperatures of nickel-based superalloys (i.e. 1300–1350 °C). The use of advanced air cooling systems coupled with thermal barrier coatings (TBCs) reduces the temperature of the underlying superalloy substrate. The bond coating, an important part of the TBC system, oxidizes to form a slow growing protective oxide layer, while also providing adhesion between the ceramic topcoat and the substrate. NiCoCrAlY overlay coatings are some of the most commonly used bond coatings for industrial gas turbines and extensive research has been undertaken over many years to find the best bond coating composition.This paper reports upon the production of new, model bond coatings with a wide range of different compositions. The focus is on their oxidation behavior at a temperature typically experienced by bond coatings on industrial turbine blades (950 °C). A physical vapor deposition technique, magnetron sputtering, has been used to deposit a range of Ni–Co–Cr–Al coatings onto 10 mm diameter sapphire substrates. This was achieved through co-sputtering two targets: a Ni–10%Cr, Ni–20%Cr, Ni–50%Cr, Ni–20%Co–40%Cr or Ni–40%Co–20%Cr target and a pure Al target. About a hundred samples with varying compositions were produced by this method. The coatings were then oxidized in air for 500 h at 950 °C.All samples were assessed by measuring the change in coating thickness, using pre- and post-exposure metrology only, and also the change in specimen weight. This approach has shown that magnetron sputtering successfully deposited 20 to 30 μm thick coatings and allowed the calculation of oxide growth rates. Energy dispersive X-ray (EDX) analysis was used to characterize the exact composition of each sample. Additionally, X-ray diffraction (XRD) has been used to identify the major oxides formed during exposure. The selective growth of protective Cr₂O₃ or Al₂O₃ or other less protective mixed oxides (depending on the initial coating composition) was observed. This influenced the oxide scale growth rate, indicating which coatings produced more protective oxides and allowing future optimization of the bond coating composition, for service within the turbine section of industrial gas turbines to be planned.     

Pseudorandom noise injection as diagnostic tool for gas metal arc welding systems

Abstract

The present work reports results obtained by applying pseudorandom noise injection to the gas metal arc welding process to determine the impulse response of the system (the response to a short pulse of energy). The phenomena having the longest time constants are investigated and it is found that there is a damped oscillation associated with delayed heating of the anode wire stickout. Properties of the oscillation are measured and found to agree with previous research. It is demonstrated that the pseudorandom noise injection technique has advantages in investigating welding processes in which it is desired to determine operating characteristics without significantly perturbing welding.     

High performance alloys for solving severe corrosion problems in flue gas desulfurization systems

Nickel-base alloys have been used as cost-effective measures in a variety of severely corrosive situations in pollution control units for coal-fired power plants. Cost-effectiveness and practical answers to corrosion problems are illustrated (specifically the “wallpaper concept”/metallic lining technique). Numerous cases of successful use of HASTELLOY® alloys in Flue Gas Desulfurization (FGD) system are listed. New developments in nickel-base alloys and their use in FGD components are discussed. In the Ni-Cr-Mo-W alloy family, C-22? alloy has the best resistance to localized corrosion in halide environments (chlorides/fluorides-containing solutions). The H-9M? alloy is the latest development in the Ni-Cr-Mo-Fe alloy family. This alloy has shown superior performance in its resistance to localized corrosion, compared to alloy 625. H-9M alloy has been tested in several FGD systems and placed in field service. This iron-containing alloy is an attractive candidate due to its moderate cost.     

基于CAN总线的焊接封闭现场有毒气体检测控制系统

设计了一种基于CAN总线焊接现场气体检测报警系统。为了解决检测系统抗干扰性能较低、节点容量较少的问题,采用以ISO/OSI模型为基础的CAN总线技术,实现了监测区域内各探测器节点与主机之间的通信。详细介绍了其工作原理和系统结构、软件模块设计。主控制器以DSPTMS320F2812为控制核心,用于处理各节点数据和人机交互;探测器以PIC16F877A为控制核心,包括气体浓度数据采集电路、CAN总线通信电路、红外标定电路。系统运行表明,系统设计合理、性能稳定,具有较强的抗干扰能力和数据通信能力。     

GOR精炼转炉烟气处理回收工艺

介绍了一种新型的GOR精炼转炉烟气处理回收的工艺流程,分析了其主要工艺设备和工艺控制特点。实践应用表明,该处理回收工艺完全能够满足GOR精炼转炉冶炼要求,粉尘处理及煤气回收达到工艺要求。     

The cadmium-rare earth systems

This program was supported by the Department of Energy through the Joint Program on Critical Compilation of Physical and Chemical Data coordinated through the Office of Standard Reference Data, National Bureau of Standards. Additional support was contributed by: Molycorp, Inc., Union Oil Co. of California, Los Angeles, CA; Reactive Metals and Alloys Corp., West Pittsburg, PA; Ronson Metals Corp., Newark, NJ; and Santoku Metal Industry Co., Ltd., Kobe, Japan. Literature searched through 1984. Professor Gschneidner is the ASM/NBS Data Program Category Editor for binary rare-earth alloys.     

Analysis of gas flow evolution and shock wave decay in detonation thermal spraying systems

The reactive Euler equations with variable gas properties are solved in both axisymmetric and plane two-dimensional flows to analyze the gas flow evolution, shock wave decay, and shock reflections in pulsed detonation thermal spraying (PDTS) systems. The gas phase governing equations are numerically solved using a high-resolution shock capturing numerical method. Expansion-compression waves are formed upon external gas expansion and persist for a long time (on the time scale of a PDTS cycle) with wide fluctuations in the gas velocity and temperature. The results show that the reflected shock wave from the substrate dies out extremely fast that micron-sized particles used in PDTS do not encounter these transients. The external shock wave decay is also analyzed for different reactive mixtures and flow geometries and is related to the truncation of the computational domain and the implementation of numerical boundary conditions at the open end boundaries.     

Structure of coatings and rubber linings exposed to operating stress in flue gas scrubbing systems

The flue gas desulphurization plants in the brown coalpower stations of RWE Energie AG operate in accordance with the limestone process. 37 scrubbers with a total of 210 000 m² steel surface are lined with a soft rubberized coating based on chloroprene base, butyl rubber/chloroprene and butyl rubber. The 110 000 m² surface of the outlet ducts is coated with synthetic resin materials based on polyester/glass flake and vinylester/glass flake spray-coatings. This paper reports on the erroneous modifications which have already occurred during a short operating period. With metallographic methods combined with light-optical and scanning electron microscopy (SEM) as well as X-ray diffraction analysis the structure of the material in the as-received condition is characterized and compared with the changes resulting from the stress due to the exposure during operation.     

浅谈纤维素焊条根焊在输气管道停气连头中的运用

近年来随着天然气输气管线的建设、投运量大幅增长,老旧输气管线的安全隐患问题日益增多,隐患整改迫在眉睫。安全隐患整改导致管线停气连头,而焊接质量是停气连头施工的重要指标,现就根焊焊接作业受到输气管线停气连头中的一些不利因数影响,浅谈纤维素焊条在停气连头中根焊中的运用。