Effects of fuel composition and temperature on fireside corrosion resistance of materials for advanced ultrasupercritical coal fired power plants

Abstract

The fireside corrosion resistance of candidate materials for the waterwalls and superheater/reheater sections of ultrasupercritical coal fired boilers have been evaluated through field testing as part of a programme cosponsored by the US Department of Energy and the Ohio Coal Development Office. The materials tested include high strength ferritic steels (SAVE12, P92, HCM12A), austenitic stainless steels (Super304H, 347HFG, HR3C), and high nickel alloys (Haynes 230, CCA617, INCONEL 740, HR6W). Protective coatings (weld overlays, diffusion coatings, laser claddings) that may be required to mitigate corrosion were also evaluated. The trials were based on previous laboratory evaluations under synthesised coal ash and flue gas conditions typical of three North American coals at temperatures ranging from 455 to 595°C for waterwall materials, while superheat/reheat materials were tested at 650–870°C. Promising materials from the laboratory tests were assembled on air cooled, retractable corrosion probes for testing in utility boilers. The probes were designed to maintain metal temperatures using multiple zones, ranging from 650 to 870°C. Three utility boilers, equipped with low NO_x burners, were identified that have adequate flue gas temperatures and represent each of the three coal types. New fireside corrosion probe results are presented for mid-western and western coal types, after approximately one year of exposure in the field. Visual examination of samples from the mid-western utility site indicated minimal evidence of significant wall loss for any of the tested materials. Samples removed from the western utility site indicated evidence of wall loss for some tested materials. Further evaluation and quantification of total metal wastage through wall thickness measurements and metallographic examination of subsurface penetration is being undertaken.     

Estimation of risk of hot corrosion in gas turbines by thermodynamic modelling

Abstract

Different types of coal fired combined cycle power systems are currently under development. However, the use of hot flue gases, originating from coal combustion or gasification, to directly drive a gas turbine may pose a problem in terms of corrosion. Cleanup of the hot gas is required in order to prevent corrosion of the turbine blading. One of the main problems associated with hot flue gases is their high alkali concentration, as alkalis are released during the coal conversion process. During the development of a hot gas cleanup protocol it is necessary to repeatedly check the effectiveness of the method in preventing hot corrosion. In the present study, thermodynamic modelling was used to estimate the risk of hot corrosion and therefore reduce the timescale and cost of the testing process. The coexistence of alkali sulphates and NiSO₄, or the formation of liquid alkali sulphates were taken as the criterion for a risk of hot corrosion. In addition, the results from coal based processes were compared to thermodynamic calculations for a well characterised gas turbine, burning fuel oil. The calculations were performed for second generation circulating pressurised fluidised bed combustion and pressurised pulverised coal combustion. In both processes, the corrosion risk, if there is any, should be much lower than the risk in a gas turbine, burning fuel oil.     

Dynamic simulation model of a coal thermoelectric plant with a flue gas desulphurisation system

In this paper a Dynamic Simulation Model has been used to present the likely responses of the electricity industries’ latest perturbations such as: changes in environmental regulations, international fuel market evolution, restriction on fuel supply and increase on fuel prices, liberalisation of the European Electricity Market, and the results of applying energy policies and official tools such as taxes and emission allowances.

The case under study refers to the Teruel Power Plant, built after the 1970s oil crisis to ensure national electricity supply; burning domestically produced coal in order to ensure local mining activity. The Teruel Power Plant has made relevant investments in order to meet emission limits, such as a Flue Gas Desulphurisation Plant. The economic viability of the power stations has to be analysed after environmental costs have been internalised.

A system is defined that studies the coal-firing Electric Power Plant selling energy to the free electricity market, whenever the generation cost is competitive. A Dynamic Simulation Model would appear to be an accurate tool to optimise power station management within different frameworks.     

生活垃圾焚烧电站烟气净化技术的应用

阐述目前我国生活垃圾的特点,提出生活垃圾焚烧的必要性,简述生活垃圾焚烧过程中所产生的烟气污染成分。根据国家对垃圾焚烧电站烟气处理的要求和排放标准,提出现阶段国内外较常运用的三种生活垃圾电站的烟气净化技术工艺,并对比其优缺点。总结出目前最受国内外欢迎的垃圾电站烟气净化技术工艺特点和应用实例,归纳出半干法烟气净化技术净化效率较高、投资和运行费用低、流程简单等优点,是一种极具发展前途的生活垃圾焚烧电站烟气净化技术工艺。     

燃煤电厂烟气中的汞浓度测量

综述了燃煤电厂烟气中各种形态汞浓度的测量方法,并对各方法的优缺点进行比较.重点介绍美国环境保护署（EPA）推荐的安大略方法（Ontario Hydro Method,简称OHM）.该方法采用等速取样、加热和防止吸附的手段,具有真实样品的代表性和准确性;采用汞的冷蒸气原子吸收原理分析汞的浓度,因而精度较高;被美国EPA和能源部（DOE）等机构推荐为美国的汞标准测试和分析方法.同时指出在中国燃煤电站采用OHM法结合汞连续在线监SCEM（Semi-Continuous Emission Monitor）法进行烟气中汞浓度现场测试和分析的实际意义.     

Full-scale simulation of flow field in ammonia-based wet flue gas desulfurization double tower

With the increasingly strict environmental requirements, sintering flue gas desulfurization in double tower had been applied to improve desulfurization efficiency and reduce the “ammonia escape” and “aerosol” phenomena. In this work, the operating conditions of a sintering plant were simulated by ANSYS CFX and the flow fields without and with fluid spray of a full-scale ammonia-based wet flue gas desulfurization (WFGD) double tower were investigated. According to the results, the evaporating tower had a profound cooling effect on flue gas with spray. The gas flow distribution was non-uniform in evaporating tower, which needed further optimizations. The flow with spray was more uniform in both towers. The pressure drop mainly took place in absorption areas of desulfurization tower. The velocity of inlet region with spray was lower than that without spray in desulfurization tower. The temperature decreased along with the forward direction of gas flow due to the heat transfer with spray in desulfurization tower. The study provided useful data for further optimization in order to achieve high desulfurization efficiency.     

Enhanced corrosion resistance of Ni/Sn nano-electrodeposited metal foam for flow field application in simulated PEMFC cathode environment

Metal foam, with large specific surface area, suffers serious corrosion problems, as flow field in proton exchange membrane fuel cell (PEMFC). Ni/Sn nanoparticles are deposited onto the surface at galvanostatic and gradient current, respectively. The morphology of coated foams is examined by scanning electron microscopy (SEM), coupled with x-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The effect of deposited current on its corrosion resistance in simulated PEMFC cathode environment is evaluated by Tafel polarization test, constant potential test and electrochemical impedance spectra. The results show that the coating effectively improved the stability of metal foam in acid environment. A uniform and dense protective film is formed by Ni/Sn electrodeposition at a gradient current density from 0 to 40 mA cm^?2. Its corrosion current at 25, 50 and 80 °C, accounts around 38.0%, 47.3% and 46.7%, respectively, of the value of uncoated metal foam. The most positive corrosion current is obtained, ?0.12 mA, which is explained to higher coating resistance (R_coat). No obvious pitting is depicted in the surface morphology after 8 h, which further proves its high corrosion resistance.     

火电厂“烟塔合一”技术及其应用

介绍了烟塔合一技术的原理及其在我国所面临的技术问题。烟塔合一技术取消了传统的火电厂烟囱,省去了烟气再热器（GGH）,使整个系统得到简化。将净烟气通过冷却塔排向大气,不仅可以降低电厂的建设费用,而且还可以提高电厂效率,降低污染。     

Stress corrosion cracking of oil and gas pipelines in near neutral pH environment: review of recent research

Abstract

Since the discovery of transgranular stress corrosion cracking (SCC) on a Canadian gas transmission line in 1985, much research has been conducted in the past 20 years. Findings of the effects of operating conditions, metallurgical and the environmental factors have been useful in preventing and mitigating failures. Several overviews of this problem can be found in the literature and the purpose of this update is to review the research results produced since the turn of the century. The recent report of SCC under static stressing conditions confirms that the cracking is indeed a true SCC process, although the rate of which is low without dynamic loading. In contrast to the high pH pipeline stress corrosion cracking in the carbonate–bicarbonate solution, this forms of cracking in dilute near neutral environment takes much longer time to initiate. Once initiated, the crack growth rate is highly sensitive to the loading rate of the applied mechanical force.     

Desulfurization reactant gas-solid coupled diffusion within CaO grain aggregate in the flue gas of coal-fired power plant

There is still room for further improvement in the SO₂ removal efficiency of dry limestone desulfurization in the coal-fired power plant. The micro-structure of limestone particle is experimentally investigated by thermogravimetric analysis, scanning electron microscopy, and Mercury porosimeter. Gaseous diffusion theory and solid-state ion diffusion theory are coupled to derive dimensionless mass transfer equations, which are verified by thermogravimetric analysis in 3,000 ppm SO₂. It is derived that solid-state ion diffusion controls the initial reaction stage. More attention should be paid to the fact that any pathway to improve solid-state ion diffusion velocity is useful for limestone desulfurization efficiency.     

燃煤电厂脱硫吸收塔出口烟道斜板立置式组合除雾装置的开发和应用

介绍了一种安装于脱硫吸收塔出口烟道或湿烟气流通烟道中的组合除雾装置的结构和原理.该除雾装置可利用烟道的原有结构进行安装,在不明显改变原系统运行阻力的同时,可以进一步脱除烟气中夹带的液滴,有效减轻相关影响.该除雾装置采用斜板立置式,由多个斜板除雾器组合而成,具有阻力小、可实现自清洗、适用性好和结构简单的特点,且结构轻巧坚固,易于维护,主要受力元件选用不锈钢材质,可有效抵御腐蚀并延长设备寿命.该除雾装置已在两个大型电站机组中应用,并取得较好的效果.     

太阳能热水系统在寒冷地区油气田倒班点的应用

介绍位于内蒙古地区乌审旗境内油气田某倒班点太阳能热水系统的应用实例,分析了太阳能热水系统在寒冷地区应用的实用性、经济性和优势,并针对该类地区的区域特点说明了系统设计应着重考虑的问题及应对措施。运行结果证明太阳能热水系统完全能够在寒冷地区推广应用．节能效果明显。     

贾汪PFBC中试电站烟气旁路减温减压装置研究设计及应用

贾汪PFBC-CC燃煤联合循环发电中试电站的烟气旁路系统是机组启动或烟气轮机甩负荷和发生故障时高温高压烟气的安全通道,旁路中的减温减压装置是其关键设备。文章对旁路烟道的减温减压装置进行了专门设计,采用新颖的高速文丘里雾化冷却器和小孔节流降压消音器相结合的方法,实现了不同工况下高温高压含尘烟气的减温减压排放。中试电站调试运行结果证明该减温减压装置系统结构紧凑,运行可靠,经济合理。