A technique for the residual life assessment of high temperature components based on creep-rupture testing on welded miniature specimens

Following the present trend in the development of advanced methodologies for residual life assessment of high temperature components operating in power plants, particularly in non destructive methods, a testing technique has been set up at ENEL/CRAM based on creep-rupture tests in argon on welded miniature specimens.

Five experimental systems for creep-rupture tests in an argon atmosphere have been set up which include high accuracy loading systems, vacuum chambers and extensometer devices.

With the aim of establishing and validating the suitability of the experimental methodology, creep-rupture and interrupted creep testing programmes have been performed on miniature specimens (2 mm diameter and 10 mm gauge length).

On the basis of experience gathered by various European research laboratories, a miniature specimen construction procedure has been developed using a laser welding technique for joining threaded heads to sample material. Moreover, a special device for removing material-reduced samples from in-service components is also in development.

Low alloy ferritic steels, such as virgin 2.25Cr1Mo, 0.5Cr 0.5Mo 0.25V, and IN 738 superalloy miniature specimens have been investigated and the results, compared with those from standard specimens, show a regular trend in deformation vs time.

Additional efforts to provide guidelines for material sampling from each plant component will be required in order to reduce uncertainties in residual life prediction.     

Coal gasification—combined cycles for electricity production

This introductory review summarizes a series of specific areas of technology which must contribute to the development of a coal gasification-combined cycle power plant. The optional combinations of the gas and steam turbines are each seen to pose different technical problems. The paramount importance of the development of a high temperature (> 1200°C) turbine inlet temperature and the subsidiary role of high temperature gas cleaning and water requirements are discussed; the prospective reliability of gasifier/boiler couplings are largely unknown.

The cost of electricity from the combined-cycle process has been shown to be most attractive in regions of high cost coal. It is considered likely that combined cycle power production will be implemented where conditions of high coal cost, low water availability and strict emission regulations coexist.

The commentary is framed in the perspective of Canadian coal resources, however most comments apply to all coal gasification combined cycle power plants and examples are drawn from all sources.     

Thermodynamic Analysis and Conceptual Design for Partial Coal Gasification Air Preheating Coal-fired Combined Cycle

The partial coal gasification air pre-heating coal-fired combined cycle (PGACC) is a cleaning coal power system, which integrates the coal gasification technology, circulating fluidized bed technology, and combined cycle technology. It has high efficiency and simple construction, and is a new selection of the cleaning coal power systems. A thermodynamic analysis of the PGACC is carried out. The effects of coal gasifying rate, pre-heating air temperature, and coal gas temperature on the performances of the power system are studied. In order to repower the power plant rated 100 MW by using the PGACC, a conceptual design is suggested. The computational results show that the PGACC is feasible for modernizing the old steam power plants and building the new cleaning power plants.     

电站风机和水泵优化检修技术的研究

介绍了电站风机与水泵优化检修技术研究与应用的一些新进展，包括电站风机与水泵的故障特征信号和故障模式、故障特征频率的计算公式、电站风机与水泵状态精密诊断专家系统、可靠性薄弱环节的统计方法、易损件的寿命管理、状态监测周期的确定、设备故障模型的识别。状态监测技术、寿命管理技术和可靠性分析技术在电站风机与水泵状态检修中的应用，为其优化检修提供了科学的依据。图1参6     

Emerging technology for component life assessment

Operating plant component damage and failure experience is reviewed. Loading conditions such as thermal stratification and striping, turbulent flow and flow-induced vibrations are often found to limit useful life, even though such loadings were typically not considered when the components were designed. High cycle thermal and mechanical fatigue are identified as important damage mechanisms. A new method of correlating fatigue data and extrapolating to the very high cycle regime is described.

The results of environmental degradation testing during the past fifteen years have shown that such effects are much more deleterious than previously assumed. Therefore environmental and aging effects must be taken into account in evaluating the reliability and dependability of components for extended periods of operation. Since most of the available data on environmental effects focus on measured crack growth rates, methods of developing improved fatigue life evaluation methods which include environmental effects on crack growth rates are now being developed.

Fatigue tests on polished specimens are characterized by nominal stress amplitudes over yield, where linear elastic fracture mechanics (da/dn vs. ΔK) methods, such as those used in the ASME Code, are not valid. The small plastic zone corrections used in the Code do not account for the plastic crack-driving energies encountered in low-cycle fatigue testing. J-integral solutions are used herein to evaluate the growth of cracks in these specimens. This approach can be shown to correlate the growth of cracks over the entire range of loading from elastic to grossly plastic conditions in widely different geometries and sizes, including the growth of very short cracks for materials of major interest in pressure vessels and piping. It can be used to correct S-N fatigue life evaluation, curves for known differences in crack growth rates whether they are due to corrosion-assisted fatigue or other variables.

Environmental effects on the crack initiation phase of fatigue failure can be directly incorporated into S-N life evaluation curves. Once the crack propagation effects are included, the resulting improved S-N curves provide a means for plant operators to evaluate the current condition of these components and systems, taking into account the cumulative damage from operating transients and cycles which the plant has experienced. The safe residual life can then be evaluated using the S-N curves to include cumulative damage for the anticipated future period of operation. This plant life evaluation approach is applicable even where in-service inspections are not feasible. It provides a sound quantitative basis for making repair/replacement decisions.     

塔式太阳能-超临界CO2发电系统集成与优化

  [目的]  传统塔式太阳能热发电效率较低,采用超临界CO₂（sCO₂）布雷顿循环集成太阳能发电可有效提高系统效率。  [方法]  采用联立方程法建立塔式太阳能集热发电（CSP）和sCO₂布雷顿循环集成系统的非线性规划数学模型以辅助系统分析与优化。模型包含太阳能集热子系统、sCO₂布雷顿循环以及高精度CO₂状态方程的约束,无需调用外部CO₂物性数据,可实现对集成系统任意数量的设计变量的同步优化。将模型应用于塔式CSP与sCO₂简单回热布雷顿循环和再压缩布雷顿循环系统的案例研究,优化系统并分析设计变量对系统效率的影响。  [结果]  研究结果表明:集成再压缩循环系统最大热效率达29.4%,高于简单循环系统的24.9%。再压缩循环的最优透平入口温度为901 K、最优膨胀比约为3;简单循环的最优透平入口温度为826 K、最优膨胀比皆大于3.2。  [结论]  系统存在最优的透平入口温度,提高透平入口温度可提高系统效率,但过高的温度会导致系统效率下降;系统存在最优膨胀比,膨胀比对集成再压缩循环系统的热效率影响较小,但对集成简单循环系统效率的影响较大。     

On the operation strategy of steam power plants working at variable load: Technical and economic issues

The context of the deregulated energy market leads to high competitiveness among producers and requires suitable strategies in plants and systems management: strongly irregular and discontinuous operation is required in order to meet the user demand and produce energy mainly during peak hours, when the electricity price is higher. This operation strategy is generally asked of all power plants, not only those traditionally devoted to load regulation and peak request, but also those originally designed to cover the base load (steam power plants, for example). As a consequence, greater income is ensured in the short term, but a reduction in the lifetime of the most critical components is likely to occur, due to creep and thermo-mechanical fatigue loadings. This will cause additional costs associated with unplanned maintenance and unavailability of the plant if a failure occurs.This paper presents a procedure aimed at evaluating this extra cost related to flexible operation, and at assisting the management decision about power plants’ operation and maintenance scheduling. The procedure, on the basis of the historical data, predicts the residual life of the most critical components, considering the effects of creep, thermo-mechanical fatigue, welding, corrosion and oxidation. It also permits one to choose different future strategies for plant management and evaluate the residual life and the economic effects for each of them. An example of application to a real steam power plant will also be presented.     

Pressure vessel steels: influence of chemical composition on irradiation sensitivity

Neutron irradiation of steels used in the construction of nuclear reactor pressure vessels can lead to the embrittlement of these materials, i.e. increasing the ductile-to-brittle transition temperature and decreasing the fracture energy, which can limit the plant life. The knowledge of irradiation embrittlement and the means for minimizing such degradation is therefore important in the field of assuring the safety of nuclear power plants.

Irradiation embrittlement is quite a complex process. It involves many variables. The most important of these are irradiation temperature, neutron fluence (neutron dose), neutron flux (neutron dose rate) and chemical composition of the irradiated material. This paper is concerned with the effect of chemical composition, i.e. the role of residual and alloying elements in the irradiation embrittlement of nuclear reactor pressure vessel steels in light water reactors. It presents a critical review for the published work in this field over the last 25 years.     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

Solar thermodynamic plants for cogenerative industrial applications in southern Europe

The paper deals with the preliminary design and optimization of cogenerative solar thermodynamic plants for industrial users. The considered plants are all based on proven parabolic trough technology, but different schemes have been analyzed: from a conventional configuration with indirect steam cycle and a heat transfer fluid such as synthetic oil or molten salts, to a more innovative arrangement with direct steam generation in the solar field. Thermodynamic parameters of the steam cycle have been optimized considering some constraints due to the heat requirements of the user, leading to a preliminary design of the main components of the system and an estimation of costs. Resulting net electric efficiency is about 10% for conventional synthetic oil plant, while 13% for innovative molten salts and DSG.A comparison with conventional solar thermodynamic systems for electricity production and photovoltaic power plants shows the economic and energetic benefits of the cogenerative solution. Cost of electricity for solar plant is cheaper of about 20 €/MWh than conventional solar power application. Moreover, heat recovery allows to achieve a further 50% of CO₂ emission savings compared to reference solar plants for only electricity production.     

燃气-超临界CO2联合循环发电系统

  [目的]  燃气轮机排气温度高,可增加底循环,利用排气的余热发电,从而提高燃料总的能量利用率。鉴于超临界CO₂循环热效率高,并且具有系统简单、结构紧凑、运行灵活等潜在优势,可与燃气轮机组成新型的燃气-超临界CO₂联合循环。  [方法]  为了充分利用燃气轮机排气余热,提出在简单回热超临界CO₂循环的基础上,再嵌套一个简单回热循环的布置方式,并以PG9351(FA)型燃气轮机为例,对其热效率进行了计算分析。同时,在系统中增加余热利用装置,可将剩余热量用于供热、转换为冷量或发电。  [结果]  结果表明:对于选定的燃气轮机,超临界CO₂循环最高温度可达约600 ℃,循环发电效率约32%,获得余热温度为170 ℃以上,余热热量占燃气轮机排气热量9%,联合循环发电效率约54%。  [结论]  燃气-超临界CO₂联合循环发电系统具有较高的热效率,并且保留部分较高品位的余热,可进一步用于电厂运行。     

安全仪表系统在二次再热机组的应用研究

  目的  安全性是电力行业永恒的主题,安全仪表系统是保证机组安全性的重要手段之一。国际上,安全仪表系统已有较为成熟的标准体系且得到广泛应用,而在国内火电行业的应用仍处于探索阶段。为推广安全仪表系统在电力行业应用,将描述其在火电二次再热机组的实际应用案例,为其它火电工程的设计、采购和运行维护提供参考。  方法  首先详细介绍和分析了相关国际规范,然后介绍了安全仪表系统在二次再热1 000 MW机组电厂项目的应用情况,并使用风险图表法对电厂进行安全完整性等级分析。  结果  通过分析等级并应用于二次再热1 000 MW机组电厂的设备招标、设计、调试、运行等,有效提高了电厂运行的安全稳定。  结论  在电力工程前期对机组安全仪表系统进行分析有利于电厂全生命周期的管理设计过程,应广泛应用于电力行业。     

Possible optimal configurations for the ZECOMIX high efficiency zero emission hydrogen and power plant

Coal use for electricity generation will continue growing in importance. In the present work the optimization of a high efficiency and zero emissions coal-fired plant, which produces both hydrogen and electricity, has been developed. The majority of this paper concerns an integration of gasification unit, which is characterized by coal hydrogasification and carbon dioxide (CO₂) separation, with a power island, where a high-hydrogen content syngas is burnt with pure oxygen stream. Another issue is the high temperature CO₂ desorption. Because of the elevated temperature heat supply, the regeneration process affects the overall performance of ZECOMIX plant. An advanced steam cycle characterized by a medium pressure steam compressor and expander has been considered for power generation. A preliminary study of different components leads to analyze possible routes for optimization of the whole plant. The plant equipped with a CO₂ capture unit could reach efficiency close to 50%. The simulations of a thermodynamic model were carried out using the software ChemCAD.

This study is a part of a larger research project, named ZECOMIX, led by ENEA (Italian Research Agency for New technologies, Energy and Environment), other partners being ANSALDO and different Italian Universities. It is aimed at analyzing an integrated hydrogen and power production plant.     

Current status of Japanese thermal power plants and life assessments of high temperature steam and gas turbine components

More than 80% of prime energy is now supplied by thermal power plants in Japan since the Great East Earthquake of 2011 and more than two thirds of them were operated for over 30 years. Evaluation of the residual life of those aged plants are, therefore, required to maintain reliability and also to avoid premature retirement. Several kinds of life assessment technologies for the high temperature components of aged steam and gas turbines have already been developed and applied to actual components. Further developments for the advanced ones are now still being conducted. The current status of Japanese thermal power plants is briefly overviewed and the life assessment technologies developed for evaluating the material degradation and component damage conditions and life extension capabilities of steam and gas turbines are explained with some examples of the applications. The differences between the development concepts and the methods developed for both turbines are also explained along with those of the design specifications.     

黄埔燃机电厂去工业化设计解析

[目的]随着城市的发展,电厂逐步由"外"向"内"发生变化,单一的建筑设计已无法满足处于城市中的电厂设计,以黄埔电厂为例,为同类型——城市型燃机电厂设计提供借鉴.[方法]通过分析、整合、利用,使多种不利因素转变为电厂去工业化的元素,丰富去工业化设计的内涵.[结果]文章分析了黄埔电厂在土地利用、建筑表皮、降噪和景观绿化等方...     

“花园式”城市型燃机电厂生态化设计研究

  目的  随着清洁电力工业的发展，燃机电厂建设成为城市区域规划的重要内容。作为一个庞大的工业建筑群体，如何塑造其形象，使其作为一个大型景观群体出现，以生态、和谐、自然、环保的积极作用为周围环境增彩成为现今燃机电厂设计的新方向和必然趋势。  方法  在燃机电厂设计之初确定全厂建筑、环境进行景观化和生态化设计的目标，对各建筑进行整体性的景观化设计，并融入生态化设计理念。  结果  以华能东莞燃机电厂为依托工程，对全厂布局优化考虑、景观化优化设计理念进行分析，打造出一个建筑新颖、景色美观、环境清新、生态良好的现代化“花园式”电厂。  结论  所提实施路径可供后续同类电厂设计参考。     

Review of conceptual design and fundamental research of molten salt reactors in China

Molten salt reactor (MSR) as 1 candidate of the generation IV advanced nuclear power systems attracted more attention in China due to its top ranked in fuel cycle and thorium utilization. Two types of MSR concepts were studied and developed in parallel, namely the MSR with liquid fuel and that with solid fuel. Abundant fundamental research including the neutronics modeling, thermal‐hydraulics modeling, safety analysis, material investigation, molten salts technologies etc. were carried out. Some analysis software such as COUPLE and FANCY were developed. Several experimental facilities like high‐temperature fluoride salt experiment loop have been constructed. Some passive residual heat removal systems were designed, and 1 test facility is under construction. The key MSR techniques including the extraction and separation of molten salt and construction of N‐base alloy have been mastered. Based on these fundamental research, Chinese Academy of Sciences has completed the design of thorium‐based MSRs with solid fuel and liquid fuel and is promoting their construction in the near future. In China, future efforts should be paid to the material, online fuel processing, Th‐U fuel cycle, component design, and construction and thermal‐hydraulic experiments for MSR, which are rather challenging nowadays.     

聚变发电站总平面布置优化

  目的  在中国聚变工程试验堆(CFETR)的概念设计过程中，厂区总平面布置意义重大，通过对厂区总平面布置面临的储能系统和布置进行比较，初步探索聚变发电厂厂区总平面的布置方案。  方法  根据聚变发电厂工艺流程、储能技术路线及储热介质的分析、研究，通过组合储能方式和布置形成了四种方案，进行了技术经济对比。  结果  熔融盐储能经济优势突出，但高温腐蚀问题对核电站安全运行影响较大，导热油方案则刚好相反。提出的储能区与核岛、常规岛的三角形布置或串联布置方案均符合总平面布置要求，并且能很好地满足全厂热力系统及储能系统热力运行流向。  结论  储能技术路线及储能区的布置是影响聚变发电厂布置的关键因素，提出的布置方案均能很好地适应新增加的储能系统热力运行，为后续聚变发电厂总平面布置提供参考。     

Life cycle assessment of an alkaline fuel cell CHP system

A life cycle assessment (LCA) of an alkaline fuel cell based domestic combined heat and power (CHP) system is presented. Literature on non-noble, monopolar cell design and stack construction was reviewed, and used to produce a life cycle inventory for the construction of a 1 kW stack. Inventories for the ancillary components of other commercial fuel cell products were consulted, and combined with information on the fuel processing requirements of alkaline cells to suggest a hypothetical balance of plant that would be required to produce AC electricity and domestic grade heat from natural gas and air.