Erosion–corrosion behaviour of Ni–20Cr plasma coating in actual boiler environment

Abstract

Erosion–corrosion is encountered in a large variety of engineering industries. In such environments, protective coatings are used. In this investigation, erosion–corrosion of the Ni–20Cr coating on nickel and iron based superalloys has been investigated by subjecting them to the boiler of coal fired thermal power plant at the temperature zone of 540°C for 1000 h duration. The erosion–corrosion kinetics of the plasma sprayed Ni–20Cr coating on different superalloys has been investigated. XRD, SEM with EDS and EPMA have been used to analyse the eroded–corroded products along the surface and cross-section. Main phases identified in all the Ni–20Cr coated superalloys after exposure are NiO, Cr₂O₃, Al₂O₃ and SiO₂. Aluminium has penetrated from the bond coat to the top coat along the splat boundaries. Oxides of chromium, nickel and aluminium are recognized as protective oxides for boiler environment. The probable mechanism of attack for Ni–20Cr coating in the given boiler environment is discussed.     

Controlling chromium vaporization from interconnects with nickel coatings in solid oxide devices

Vaporization of Cr-rich volatile species from interconnect materials is a major source of degradation that limits the lifetime of planar solid oxide devices (solid oxide fuel cells and solid oxide electrolysis cells) with metallic interconnects. Some metallic coatings (Ni, Co, and Cu) may significantly reduce the Cr release from interconnects and slow down the oxide scale growth on the steel substrate. To shed additional light upon the mechanisms of such protection and find a suitable coating material for ferritic stainless steel materials widely used for interconnects, we used a combination of first-principles calculations, thermodynamics, and diffusion modeling to investigate which factors determine the quality of the Ni metallic coatings. We found that Cr migration in Ni coatings is determined by a delicate combination of the nickel oxidation, Cr diffusion, and phase transformation processes. Although the formation of Cr₂O₃ is more exothermic than that of NiO, the kinetic rate of the chromia formation in the coating layer and its surface is significantly reduced by the low mobility of Cr in nickel oxide and in NiCr₂O₄ spinel. These results are in a good agreement with diffusion modeling for Cr diffusion through the Ni coating layer on the ferritic 441 steel substrate and available experimental data.     

废旧含氯塑料热解及其能源利用研究

存在于城市生活垃圾中的含氯塑料（如PVC等）是造成垃圾焚烧电站设备腐蚀和二次污染的主要因素。本文对利用热重－差分分析仪对氯含量53．8％聚氯乙烯（PVC）和无氯高密度聚乙烯（HDPE）以及氯含量10％－46％氯化聚乙烯（CPE）热解特性进行了研究。根据含氯塑料分级热解的实验结果,提出了含氯塑料热解与残余物燃烧的工艺路线,并对基于该工艺路线的概念电站的性能进行了计算和分析。     

基于Fluent的某型号锅炉末级过热器流动特性数值研究

针对某型号锅炉末级过热器的泄漏情况,基于CFD软件FLUENT,建立过热器的二维模型,采用k-ε湍流模型对烟气的速度场和离散项颗粒的轨迹场进行了数值模型。针对末级过热器管道多根管道密集布置的狭小空间,定量分析炉管黑线烟气流速分布的差异,颗粒的速度场及其轨迹特点,可为进一步研究锅炉末级过热器管道的剩余寿命提供理论依据。     

EVT垃圾焚烧系统燃烧设备

本文从垃圾料系统,焚烧炉排型式和燃烧调整等方面,介绍德国ＥＶＴ公司的垃圾焚烧系统燃烧设备,分析了燃烧设备的特点。     

Energy from municipal solid waste: A comparison with coal combustion technology

The conversion of municipal solid waste (MSW) to energy can conserve more valuable fuels and improve the environment by lessening the amount of waste that must be landfilled and by conserving energy and natural resources. The importance of utilizing MSW was recognized in the 1991 U.S. National Energy Strategy, which sought to “support the conversion of municipal solid waste to energy.” One route to utilizing the energy value of MSW is to burn it in a steam power plant to generate electricity. Coal has long been the predominant source of energy for electricity production in the U.S.; therefore, a considerable science and technology base related to coal combustion and emissions control can be, and has been, applied with substantial benefit to MSW combustion. This paper compares the combustion of coal and MSW in terms of fuel characteristics, combustion technology, emissions, and ash utilization/disposal. Co-combustion of coal and MSW is also discussed. MSW issues that can be addressed by research and development are provided.The major environmental issues that designers of MSW combustion systems have had to address are emissions of trace organic compounds, particularly polychlorinated dioxins and furans, and trace elements such as mercury, lead, and cadmium. Emission of trace organics is generally the result of a poorly designed and/or operated combustion system; modern MSW systems use good combustion practices that destroy organic compounds during the combustion process. Proper control of air/fuel mixing and temperature, and avoidance of “quench” zones in the furnace, help to ensure that potentially harmful organics are not emitted. Computer codes and other design and troubleshooting tools that were developed for coal combustion systems have been applied to improve the performance of waste-to-energy systems.Trace element emissions from both coal and MSW combustion result primarily from vaporization of elements during the combustion process. Most of the trace elements that are vaporized condense on fly ash as the combustion products cool downstream of the furnace and can be effectively controlled by using an efficient particulate removal device. However, volatile elements, particularly mercury, are emitted as a vapor. Several mechanisms are available to capture mercury vapor and some are in use. The development of satisfactory control technology for mercury is a topic currently of high interest in coal burning.The potential for leaching of trace elements and organics from MSW residues after disposal raises issues about the classification and management of ash. Results of laboratory leaching tests, especially for lead and cadmium, have not been consistently supported by field experience. Careful interpretation of the available test protocols is needed to make sure that residues are properly managed.Because of the large scale of coal-fired boilers for electricity production, co-firing of MSW with coal in such boilers could consume large quantities of waste. Several short-term demonstrations have shown that co-firing is feasible. The issues involved in co-firing are emissions of trace elements, trace organics, and acid gases; boiler slagging and fouling; and long-term effects, such as corrosion and erosion of boiler tubes.Areas where research and development has contributed to improved MSW combustion include (a) the formation mechanisms of polychlorinated dioxins/furans, especially low-temperature, catalytic mechanisms, (b) methods of combustion air distribution in incinerators that result in better combustion and reduced emission of organic compounds, (c) the use of gas reburning to control NOx and reduce emission of organic compounds, (d) practical methods for removing organic compounds and mercury from MSW flue gas, (e) the performance of electrostatic precipitators in removing MSW fly ash, particularly when co-firing MSW and coal in existing coal-fired boilers, and (f) burning MSW in fluidized beds or of pulverizing refuse-derived fuel and firing it in suspension-fired, pulverized coal boilers.     

丙烯腈装置焚烧炉余热回收利用的分析

对丙烯腈装置旧焚烧炉焚烧废水后产生的余热在能源利用方面存在不合理的地方进行了介绍,提出了通过增设一台卧式焚烧炉,利用导热油作为热载体,对废水焚烧后产生的余热进行回收利用的方案,对余热回收系统在运行过程中产生的导热油炉管腐蚀和炉管结垢的问题及原因进行了阐述,通过改变废水焚烧流程实现不同的废水分开焚烧的办法解决了炉管腐蚀的问题,在新焚烧炉增设吹灰器的办法解决了炉管结垢问题,达到了合理利用焚烧炉余热的目的。     

Applying Low-Pressure Plasma Spray (LPPS) for coatings in low-temperature SOFC

Low-temperature solid oxide fuel cell (LTSOFC) has shown great potentials for commercial applications in clean energy generation. Seeking for low cost and easy fabrication method is one of the most important issues for LTSOFC investigations. This paper introduces a new coating spray technology, namely Low-Pressure Plasma Spray (LPPS), for efficiently manufacturing different functional coatings of LTSOFC. By applying the LPPS technique, uniform and dense Ni_0.8Co_0.15Al_0.05LiO_2?δ (NCAL) coatings were made on both solid bipolar plates and porous nickel foams to perform as protecting coatings and electrode catalyst coatings respectively. Microstructure study showed that multi phases were formed and in-situ nano-micro crystallization occurred in the coatings during the LPPS process. Around 30 W output was achieved in a 4-cell stack indicating that the LPPS sprayed NCAL coatings on bipolar plates worked well. A fuel cell based on the NCAL-coated Ni foam reached an open circuit voltage (OCV) at 1.08 V and a maximum power density of 717 mW cm^?2 at 550 °C. This study reveals that LPPS is a promising technology for fabricating coatings of LTSOFC.     

Comparison of solid oxide fuel cell anode coatings prepared from different feedstock powders by atmospheric plasma spray method

Atmospheric plasma spray (APS) deposition of a high-performance anode coating, which is essential for obtaining high power density from a solid oxide fuel cell (SOFC), is developed. A conventional, micron-sized, nickel-coated graphite – yttria stabilized zirconia (YSZ) – graphite blend feedstock leads to a non-uniform layered coating microstructure due to the difference in the physical and thermo-physical properties of the components. In this research, new types of feedstock material received from a spray-drying method, which includes nano-components of NiO and YSZ (300 nm), are used. The microstructure and mechanical properties of a coating containing a nano composite that is prepared from spray-dried powders are evaluated and compared with those of a coating prepared from blended powder feedstock. The coating microstructures are characterized for uniformity, mechanical properties and electrical conductivity. The coatings prepared from spray-dried powders are better as they provide larger three-phase boundaries for hydrogen oxidation and are expected to have lower polarization losses in SOFC anode applications than those of coatings prepared from blended feedstock.     

Long term creep properties and microstructure of SUPER304H,TP347HFG and HR3C for A-USC boilers

Abstract

SUPER304H (18Cr–9Ni–3Cu–Nb–N; ASME CC2328) and TP347HFG (18Cr–12Ni–Nb; ASME SA213) have been developed for high strength oxidation resistant steel tubes to operate at high steam temperatures and pressures. The longest creep rupture tests performed to date (600°C for 85 426 h for SUPER304H; 700°C for 55 858 h for TP347HFG) showed that the stable strength and microstructure were retained, with very little formation of σ-phase compared with conventional austenitic stainless steels and no other brittle phases. The alloy HR3C (25Cr–20Ni–Nb–N; ASME CC2115) has been developed for the high strength and high corrosion resistant steel tubes used in recent ultrasupercritical (USC) boilers with steam temperatures of ～600°C. The longest creep test conducted to date (700°C, 69 MPa for 88 362 h) confirmed a stable creep strength and microstructure at 600–800°C. Superheater and reheater tubes of these alloys installed in the Eddystone No.1 USC power plant since 1991 have been removed and investigated. Updated long term creep rupture properties of the steels and microstructural changes during service are reported. Three steel tubes have been successfully applied as standard materials for superheater and reheater tubes in newly built USC boilers.     

Evaluation of the corrosion resistance of Ni(P)Cr coatings for bipolar plates by electrochemical impedance spectroscopy

In the present research, the corrosion resistance of Ni–P and Ni–P–Cr coatings on AA7075-T6 aluminum plates under simulated anodic and cathodic conditions of polymer electrolyte membrane fuel cells (PEMFC) has been studied by electrochemical impedance spectroscopy (EIS). Three Ni–P coatings 20 μm, 30 μm, and 40 μm thick applied by electroless deposition were tested. Besides, a two-layer Ni–P–Cr coating 30 μm thick was also analyzed. It was formed by an inner Ni–P layer, and an outer 10 μm thick chromium one added by electroplating. Corrosion tests were combined with interfacial contact resistance (ICR), roughness, contact angle, and SEM-EDX measurements. The best results were obtained for the 20 μm Ni–P and the two-layer Ni–P–Cr coatings, although the latter showed a high ICR value due to the high electrical resistivity of the chromium oxide surface formed. It was verified that coating degradation occurs when the electrolyte penetrates the micro-cracks and the nodular surface interfaces, reaching the base metal and causing the coating delamination. This behavior is associated with a sharp decrease in the polarization resistance (R_p) of the equivalent circuit model fitted to the EIS results.     

A 7 year long measurement period investigating the correlation of corrosion,deposit and fuel in a biomass fired circulated fluidized bed boiler

The present investigation involves a unique, 7 year (2001–2007) long study of corrosion and deposits on superheater tubes in a biomass fired circulated fluidized bed boiler. These measurements are correlated against the different fuels used over this period. In the earlier years, the boiler was run with a mixture of different biomass fuels and peat. In later years, recycled wood was introduced into the fuel mix. The deposit growth rate approximately doubled when the recycled wood content of the fuel was increased to 10–20%. Small amounts of chlorine and zinc were found both in the recycled wood and in the deposit layer. These elements together with alkali metals from the biomass, have the potential to form sticky compounds that increase the deposit growth rate. The corrosion rate of the superheater tubes varied over the study period. A number of possible explanations for this phenomenon are discussed.     

耐高温磨蚀涂层在循环流化床锅炉中的应用

循环流化床锅炉是一种节能、环保的新型锅炉 ,但却存在着磨损、腐蚀非常严重的问题。大量研究表明 ,表面涂层技术是解决循环流化床锅炉高温磨蚀问题的一种最经济有效的方法。综述了目前国内外常用的几种循环流化床锅炉耐高温磨蚀涂层 ,对各种涂层的研究应用现状、性能等作了简要分析。结果表明 ,高铬合金涂层和金属 /陶瓷复合涂层以及高速电弧喷涂粉芯丝材工艺具有广阔的应用前景。     

Oxidation of MCrAlY coatings on Ni based superalloys

Abstract

Industrial gas turbine engines used for power generation generally employ Ni based superalloys for the turbine blades. The operating conditions for these blades are very arduous with high temperatures (>900°C) leading to oxidation and corrosion. Therefore in order to increase the service life of components, coatings are employed which allow the use of Ni based superalloys at higher temperatures and therefore more efficient engines. These systems are very complicated and in order to understand coating performance and service life, many modelling approaches have been utilised. However, there is still a lack of understanding of the thermally grown oxide (TGO) with regards to its chemistry, microstructure, adhesion strength and mechanical properties. Therefore a more detailed understanding of the TGO would be useful for both empirical and computational modelling. The effect of compositional changes in the MCrAlY bond coat and their effect on the TGO have been studied. Two different MCrAlY coatings have been examined after aging at representative operation temperatures. A number of analytical techniques have been used including, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray and electron backscattered diffraction. A dual beam scanning electron microscope has also been utilised for both TEM sample preparation and microstructural evaluation. These techniques will allow a better understanding of the microstructure of the TGO, ultimately leading to improved predictions of coating behaviour and service life.     

Fabrication and properties of anode-supported tubular solid oxide fuel cells

Tubular solid oxide fuel cell (SOFC) systems have many desirable characteristics over their planar counter-parts. Anode-supported tubes provide an excellent platform for individual cells. They allow for a thin electrolyte layer to be applied to the outside of the tube, which helps to minimize polarization losses. This paper describes the fabrication of nickel–zirconia (Ni–YSZ)-based anode tubes via extrusion of a plastic mass through a die of the required dimensions. The anode tubes were then dried and fired. Tests were performed on the tubes to determine the effects of firing temperature on porosity to allow for a pinhole-free electrolyte coating to be applied. Thin layer coating techniques, including vacuum-assisted dip coating and painting, were compared. Ni–YSZ anode-supported tubular SOFCs with a gas-tight thin YSZ electrolyte layer were then realized. Microstructure of the anode support, electrolyte and cathode thin films was also examined.     

SiCrOxNy选择性吸收涂层制备及性能研究

采用直流及中频反应溅射在铜基底上沉积SiCrO_xN_y光谱选择性吸收涂层。对该涂层的光学性能进行表征,其吸收比为0.938,80℃发射比为0.07。经300℃,200 h热处理后,吸收比无明显变化,发射比小幅升高;俄歇电子能谱(AES)分析显示,界面处元素扩散和Cu基底氧化是涂层光学性能下降的主要原因。在35℃下进行5%盐雾腐蚀试验,腐蚀初期涂层发射比迅速升高,腐蚀36 h后吸收比衰减加速,涂层表面开始出现剥落现象;致密的SiO2减反射层对增强涂层耐盐雾腐蚀性能有明显效果。     

Investigation of corrosion properties with Ni–P/TiNO coating on aluminum alloy bipolar plates in proton exchange membrane fuel cell

Aluminum alloy bipolar plates have unique application potential in proton exchange membrane fuel cell (PEMFC) due to the characteristics of lightweight and low cost. However, extreme susceptibility to corrosion in PEMFC operation condition limits the application. To promote the corrosion resistance of aluminum alloy bipolar plates, a Ni–P/TiNO coating was prepared by electroless plating and closed field unbalanced magnetron sputter ion plating (CFUMSIP) technology on the 6061 Al substrate. The research results show that Ni–P interlayer improves the deposition effect of TiNO outer layer and increase the content of TiN and TiO_xN_y phases. Compared to Ni–P and TiNO single-layer coatings, the Ni–P/TiNO coating samples exhibited the lowest current density value of (1.10 ± 0.02) × 10^?6 A·cm^?2 in simulated PEMFC cathode environment. Additionally, potential cyclic polarization measurements were carried out aiming to evaluate the durability of the aluminum alloy bipolar plate during the PEMFC start-up/shut-up process. The results illustrate that the Ni–P/TiNO coating samples exhibit excellent stability and corrosion resistance.     

生活垃圾焚烧厂脱硝技术探讨

通过分析生活垃圾焚烧厂NOx生成机理、NOx脱除技术以及国内外垃圾电厂脱硝现状并结合我国具体情况,探讨适合我国生活垃圾焚烧厂切实可行的脱硝技术,为"十二五,,及将来我国生活垃圾焚烧厂开展烟气脱硝工作提供借鉴.     

垃圾焚烧炉燃烧技术及设备的发展

本文回顾了垃圾焚烧炉燃烧技术及设备的发展历史,分析了各种燃烧设备的特点,进而对我国的垃圾焚烧技术和设备的发展提出了建议。     

Cu doped Ni–Co spinel protective coatings for solid oxide fuel cell interconnects application

Four different amount of Cu doped Ni–Co alloy coatings were fabricated on SUS430 substrate by electroplating for solid oxide fuel cells (SOFCs) interconnects application. After oxidation at 800 °C, the microstructure and oxide phase of samples were tested by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Our experimental results indicated that the Cu addition improved the electrical behavior of Ni–Co alloy coating. Cu doping reduced the activation energy (Ea) of electrons hopping and inhibited the growth of Cr₂O₃ oxide layer. Furthermore, the oxidation kinetics and electrical properties of the alloy coatings were obtained. These results showed that the 9% Cu doped Ni–Co coated steels achieved the minimum parabolic rate constant (2.05 × 10⁻¹⁴ g²cm⁻⁴s⁻¹) and area specific resistance (14.11 mΩ cm²) after the thermostatic oxidation process.