Time related temperature field over a reactor internal surface

In the synfuels production business, reactors that are subjected to thermal and mechanical loads are used. These reactors are continously cooled by means of internal water jackets. The jackets have been subjected to structural failures resulting from thermal fatigue. It was important to map the time dependent temperature field in reality.

A comprehensive test programme has been conducted on an operating reactor for a period of 10 months. A network of 120 thermocouples, were installed in the jacket in order to map the temperature field over the jacket, having a developed area of about 12 m × 6,4 m and link it with the associated reaction process. In addition a finer grid consisting of 46 inner surface thermocouples, were used in the test.

The results obtained were somewhat surprising: The measured temperature field, over the inner surface of the jacket is essential asymmetric. Looking at the vertical distribution of individual generators of the cylindrical jacket, it seems that two generators indicated higher temperatures than the average. In general, hotsports are generated at these generators lower part and gradually move toward the top of the reactor. The appearance and disappearance of hot spots seem to be random for 1 to 5 minutes all over the inner surface of the jacket. They have higher frequency adjacent to the hotter generators. Cold spots having temperatures around 230 °C, which is the temperature of the cooling water are more numerous, over larger areas and have a duration of about 15 to 30 minutes. The results indicated that there are not “hot bands” in the jacket, as opposed to what was assumed before the test.

The time dependent temperature field was processed and presented on a computer screen.     

Analytical and numerical crack growth prediction for a leak-before-break assessment of a nuclear pressure vessel

Extending the safety analysis of a nuclear reactor pressure vessel beyond the requirements of the regulations which were first laid down in the ASME-Code, the behavior of two crack sizes (1/4-t axial, 3/4-t circumferential, a/2c = 1/6) in the upper shelf region is analyzed to demonstrate the capability of a reactor pressure vessel for Leak-Before-Break. The postulated load is a monotonic increase of pressure, ending when the crack penetrates through the wall.

The conditions for re-initiation and ductile extension of the conservatively postulated largest possible axial and circumferential crack geometries resulting from initiation and arrest during a thermal shock are evaluated on the basis of the J-integral concept. Three-dimensional finite element models simulating large amounts of crack growth are employed as well as analytical approximations. The results demonstrate that very high internal pressure far beyond the capacity of the plant and also far beyond the strength of the other components of the primary circuit would be required to initiate and grow the cracks, and that Leak-Before-Break behavior is confirmed.     

Nuclear methane reforming for coal gasification

The G.E.G.N. (Groupement pour l'Etude de la Gazéification Nucléaire) is a group which will study nuclear coal gasification and which is formed by “Commissariat à l'Energie Atomique”, “Gaz de France”, “Charbonnages de France”, “Creusot-Loire” and “Novatome”. The G.E.G.N. was created in 1976, with the approval of the French government, to determine a coal gasification process, to define a R & D programme and to evaluate the cost of the process.

The nuclear steam reforming of methane and the hydrogasification of coal were chosen as preliminary options. The hydrogasification was also chosen because the temperatue level of the steam reforming is lower than that of the coal steam gasification.

Therefore, it seems reasonable to limit the core outlet temperature to 850°C, although the core can deliver higher helium temperatures.

The use of an intermediate circuit allows a great flexibility in the reformer design and makes it easier to handle the catalyst.

In this paper the reasons for these choices are explained and the technological solutions are discussed.     

A focused approach to reliability, availability and maintainability for critical pressure vessels

A “Review Integrity of Critical Equipment” (RICE) programme is presented here. The programme has a systematic structure that facilitates the development of strategic maintenance plans for critical pressure vessels. The programme is based on the reliability, availability and maintainability (RAM)‘ principles and was developed and applied to Sasol's vessels in order to ensure compliance with future statutory requirements. It is believed that the presented programme will be useful for other users than Sasol.

The programme consists of a number of stages; systematic data acquisition, assessment of data and proposed principle inspection plan, acceptance of the plan followed by detailed planning, actual inspection and evaluation of results. The inspection plan is supplemented by proactive measures to solve suspected problems. The paper includes a case study of a critical scrubber vessel in order to illustrate how the programme works.     

The use of waste heat in a solar still

There are instances in remote areas where heat is being wasted, e.g., in internal combustion, engines, etc. Some of this heat can be recovered to produce distilled water in solar stills.

The solar still replaces the cooling tower, ponds, or radiators normally used to control the engine temperature. The diesel cooling water in such a system remains separate from the saline water in the solar still.

The advantages of using such a system compared with a conventional solar still are:

1. (a) water costs are very much reduced

2. (b) the area occupied is much less, i.e., about 1/5th

3. (c) production has much less seasonal variation

4. (d) the efficiency of the solar still is improved due to the higher operating temperatures.

From experiments conducted at Highett using a Mk VI solar still fitted with a simple heat exchanger and a separate electrically-heated source of hot water to simulate the waste heat, design data are not available for application to working systems. The information required to match a solar still to a diesel's cooling requirement is:

1. (a) engine efficiency

2. (b) hourly fuel consumption

3. (c) hourly solar radiation

4. (d) hourly ambient temperatures.

A by-product of this work has been the production of a “solar water heater” which costs less than that of the cheapest conventional system. This “solar” hot water system uses a heat exchanger similar to what is used to transfer the waste heat to the saline water. It is envisaged to have hot water productions approximately the same as the distilled water productions. The influence of hot water production on the output of the waste heat solar still is discussed.     

Japan''s nuclear energy policy: from firm commitment to difficult dilemma addressing growing stocks of plutonium, program delays, domestic opposition and international pressure

Since 1956, Japan has been on a path to reduce its dependence on foreign energy sources through the development of nuclear power. This paper examines the origins of this commitment, the changing social issues and the current dilemma Japan faces regarding the future of its nuclear energy policy and its efforts to overcome the domestic and international pressures to ensure safety and security.

Galvanized by international initiatives and further motivated by the oil crises in the 1970s, Japan's commitment to develop a closed nuclear fuel cycle, one which reprocesses fuel from thermal reactors for use in advanced fast breeder reactors, has remained resolute. However, program delays, international security concerns over the plutonium, a weapons-grade nuclear material and one of the products of reprocessing, and increasing public opposition to various components of the Atomic Energy Commissions’ Long-Term Program for Development and Utilization of Nuclear Energy, have put pressure on the government to resolve these issues.

The commitment to develop the technology on one hand is commendable however it has contributed to the dilemma the Japanese nuclear industry now faces: a growing stockpile of plutonium and no readily available means of reducing it. With growing public involvement, finding a straightforward technology solution is increasingly difficult.

In 1995, an accident at Monju, one of the first prototype fast breeder reactors in Japan, prompted the Commission to initiate the first Roundtable Conference. The purpose of the Conference was to open the policy making process in an effort to determine a “national consensus” on nuclear energy. Further accidents and on-going opposition further slowed the implementation of the Program, however, in the latest Program, released in 2000, the Commission attempts to address these issues while building in a new style of flexibility in order to allow for greater options in the future.     

海上风电导管架群桩施工技术的研究应用

  [目的]  由于目前我国海上风电工程尚未推广应用导管架群桩结构形式基础,还没有导管架群桩基础施工的成熟技术,为了填补该项施工技术空白,也为了解决国内首例导管架四桩型式基础在珠海桂山风电项目的桩基定位控制难题和倾斜度控制难题,特对该项工艺技术进行了探索研究。  [方法]  针对珠海桂山海上风电项目的特殊水文、地质和风浪等海况进行了分析,反复推敲国际案例,研究定位测量技术,邀请行业专家论证,最终设计出了一套导管架四桩基础空间位置精确定位、倾斜度精确控制、水下多点对接安装的关键成套技术,并设计了一套桩基施工工装用以辅助群桩施工。  [结果]  该套技术方案功能包括双层导向架着床精确定位调平、下层导向架插桩限位、双层液压千斤顶联动调整钢桩倾斜度和RTK GPS搭配全站仪测控系统实时追踪指引导管架与水下桩基多点对接安装,已成功地应用于广东珠海桂山海上风电示范项目,优化了设计工序,高效率、高质量、高精度地完成了全部导管架四桩基础的施工,为整个风电场项目的快速推进争取了更多的宝贵时间,为项目后续风机安装、海缆敷设和并网发电等工作的快速展开做好了准备。  [结论]  该套技术实现了海上风电导管架群桩型式基础在国内由理论研究转换为工程实践的重大突破,解决了导管架群桩型式基础在海上风电工程的精确成桩技术难题,为后续海上风电场导管架群桩基础技术的推广应用作了技术储备和经验推广。     

Measurement and analysis programme within the thousand roofs programme

The BMFT and the State governments jointly started a “Thousand Roofs Programme” in September 1990. At first, this programme was limited to the territory of the former West Germany. In July 1991, the extension to the new federal States was announced. In the programme the installation of 2,250 small (1–5 kWp) grid-connected PV systems on the roofs of one or two-family houses is being sponsored. Federal and State grants were provided for the actual system costs to an upper limit of DM 27,000 per kWp. The grant proportion was 70%, 50% of the system cost from Federal and 20% from State funds.     

Creep test of type 304 stainless steel tube containing a notch subjected to internal pressure

This paper summarises the results of experimental creep tests of type 304 stainless steel tube subjected to internal pressure at 650°C. The equipment used was especially developed for these tests.

The tubes without notches were tested at pressures of 9·32 and 7·36 MPa. Test results indicate that the rupture time of the tubes without notches is in good agreement with that of uniaxial specimens when the maximum stress is taken as the rupture criterion. The tubes containing axial and circumferential surface notches were tested at a pressure of 7·36 MPa. Test results indicate that the ductile fracture theory is applicable to the life prediction in the case of axial notches.

An electric potential method was very useful for monitoring the creep crack growth from the notch root. The relationship between the creep crack growth rate and the fracture mechanics parameter, σ_net or K₁, was investigated.     

Intergranular susceptibility in failures of high pressure tubes

This work addresses the influence of metallurgical susceptibility to intergranular cracking on the repeated cracking and failure of thick wall curved steel tubes from a petrochemical reactor. These tubes are made of HP-4 steel, bent and heat treated, and then subjected to autofrettage. Internal pressure is around 250 MPa. All failures are characterized by strongly branched, mostly circumferential multiple intergranular cracks. Most cracks initiated in the outer surface, in contact with steam; these were related to stress corrosion cracking (SCC). Some cracks initiated in pre defects in the inner surface, in contact with a polymer, and in the mid thickness of the tube wall. This study includes the assessment of deformation and temperature induced embrittlement mechanisms, measurement of longitudinal residual stresses, and mechanical testing included tensile, Charpy and SCC tests. Susceptibility to intergranular cracking was experimentally assessed by recreating conditions of embrittlement by thermal treatments and tensile testing. Samples with 0, 3 and 5% plastic deformations were subjected to 24 h thermal treatments between 300 and 400 °C. Under the conditions of previous plastic deformation due to bending and autofrettage it was possible to recreate intergranular embrittlement at service temperatures, a phenomenon similar to temper embrittlement. The process of forming the bent created localized yielding and large longitudinal residual stresses. Recovery measures, mostly relying on thermal treatments, were defined.     

Assessment of thermal stresses and ratchetting in reactor vessels

Reactor vessels are often subject to “hot spots” developing at certain positions on the shell, which, if they are of a cyclic nature, may result in strain growth and fatigue failure if the amplitude of the cyclic strains are not restricted.

The paper deals with an investigation of a particular vessel with the object of determining the characteristics of “hot spots” that would cause cyclic plasticity or ratchetting in order to determine the limiting criteria to avoid or restrict such effects onder continuous operational conditions.

The basis of the investigation is finite element analysis. Temperature dependent elasto-plastic material properties are taken into account and the mesh is refined in selected “hot spot” positions in order to obtain accurate strain and stress states under cyclic loading conditions.

The assessment criteria are discussed which are the basis of recommendations for continuous operation under cyclic conditions.     

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.     

Wood pellet production costs under Austrian and in comparison to Swedish framework conditions

Owing to the rapidly increasing importance of pellets as high-quality biomass fuel in Austria and Europe within the last years, many companies, mainly from the wood industry, are thinking of entering this market. The calculation of the production costs before starting a pellet plant is essential for an economic operation. Based on comprehensive investigations within the EU-ALTENER project “An Integrated European Market for Densified Biomass Fuels” calculations of the pellet production costs loco factory for different framework conditions with basic data based on already realised plants as well as a questionnaire survey of pellet producers in Austria, South Tyrol and Sweden have been performed.

The production costs for wood pellets are mainly influenced by the raw material costs and, in the case of using wet raw materials, by the drying costs. Depending on the framework conditions these two parameters can contribute up to one-third of the total pellet production costs. Other important parameters influencing the pellet production costs are the plant utilisation (number of shifts per week) as well as the availability of the plant. For an economic production of wood pellets at least three shifts per day at 5 days per week are necessary. An optimum would be an operation at 7 days per week. A low plant availability also leads to greatly increased pellet production costs. A plant availability of 85–90% should therefore be achieved.

The calculations show that a wood pellet production is possible both in small-scale (production rates of some hundred tonnes per year) as well as in large-scale plants (some ten thousand tonnes per year). However, especially for small-scale units it is very important to take care of the specific framework conditions of the producer, because the risk of a non-economic pellet production is considerably higher than for large-scale systems.

The direct comparison of typical pellet production costs in Austria and Sweden showed the Swedish pellet production costs to be considerably lower due to larger plant capacities, the combination of pellet production and biomass CHP or biomass district heating plants and the implementation of technologies which allow an efficient heat recovery from the dryers. Moreover, another difference between the Austrian and the Swedish framework conditions is the price of electricity, which is much lower in Sweden.     

Thermic diode solar panels for space heating

Thermic diode solar panels are a new method of heating buildings using solar energy. Each panel combines all the necessary elements of a complete solar energy system (collector, controls, storage heat exchangers and ducting) into a single module. They have no moving parts and they need no external power. Panal operation is discussed and thermic panels are compared to other typical solar heating systems: air heating, water heating, active and passive. Residential and commercial applications are also discussed.

The performance of thermic panels are compared to conventional solar systems. A computer simulation of thermic panels in a residential space-heating application resulted in predictions of the percentage of solar heat provided by the panels. The predictions are compared to similar analyses of conventional solar systems. Thermic panels did as well or better than conventional systems in the six climate types investigated. However, since their installed cost is less, they are expected to be more economic than conventional solar systems.

Thermic panels improve the economics of flat-plate collectors by their modularity and simplicity. Modularity reduces installation costs and raw materials cost; simplicity reduces maintenance costs. Furthermore, the panels can be integrated into the buildings structure, saving the cost of the wall or roof elements they replace.     

Metal dusting failures in methane reforming plant

The Mossgas plant converts natural gas from sub-sea wells located 85 km south of Mossel Bay, to synthetic fuels. The methane rich natural gas is reformed to syngas by reaction with steam and oxygen at very high temperatures over a nickel catalyst in the secondary reformer to provide feedstock for the subsequent Fischer-Tropsch reaction in circulating bed catalyst reactors.

The gas composition and temperature during reforming are within the carburising range and metallic components in some parts of the reforming system are thus susceptible to degradation by a mechanism of accelerated carburisation known as “metal dusting”. Failure of an Alloy 600 component in the reformer neck due to metal dusting, and the subsequent catastrophic failure of the reformer shell is described.

The mechanism of metal dusting is briefly reviewed with specific reference to the comparative resistance of various metallic materials to this form of degradation. The Mossgas experience in this respect appears to contradict some of the limited data that has so far been published on the topic in that Alloy 800 has been found to vastly out-perform the high nickel Alloy 600 in this specific process environment. Further alloy exposure programmes have been initiated in order to try to gain a greater understanding of the practical limitations of metallic materials to this environment.     

CIRCUMFERENTIAL CRACK PROBLEM FOR AN FGM CYLINDER UNDER THERMAL STRESSES

The main objective of this study is to determine the stress intensity factors associated with a circumferential crack in a thin-walled cylinder subjected to quasi-static thermal loading. The cylinder is assumed to be a functionally graded material. In order to make the problem analytically tractable, the thin-walled cylinder is modeled as a layer on an elastic foundation whose thermal and mechanical properties are exponential functions of the thickness coordinate. Hence a plane strain crack problem is obtained. First temperature and thermal stress distributions for a crack-free layer are determined. Then using these solutions, the crack problem is reduced to a local perturbation problem where the only nonzero loads are the crack surface tractions. Both internal and edge cracks are considered. Stress intensity factors are computed as functions of crack geometry, material properties, and time.     

Deterministic assessment of reactor pressure vessel integrity under pressurised thermal shock

Numerical investigations were carried out to assess the integrity of reactor pressure vessels under pressurised thermal shock (PTS). The 4-loop reactor pressure vessel with cladding was subjected to thermo-mechanical loading owing to loss of coolant accident. The loss of coolant accident corresponding to small break as well as hot leg breaks were considered separately, which led to axisymmetric and asymmetric thermal loading conditions respectively. Three different crack configurations, 360° circumferential part through, circumferential semi-elliptical surface and circumferential semi-elliptical under-clad cracks, were postulated in the reactor pressure vessel. Finite element method was used as a tool for transient thermo-elastic analysis. The various fracture parameters such as crack mouth opening displacement (CMOD), stress intensity factor (SIF), nil ductility transition temperature (RT_NDT) etc. were computed for each crack configuration subjected to various type of loading conditions. Finally for each crack a fracture assessment was performed concerning crack initiation based on the fracture toughness curve. The required material RT_NDT was evaluated to avoid crack initiation.     

平行流式电机周向水套结构参数对散热性能影响研究

针对电力机车上某功率密度为1.27 kW/kg的平行流式电机周向水套结构的散热问题进行了研究。首先利用热阻网络法建立了平行流多通道截面的热阻数学模型;然后借助FLUENT软件对水套的电机散热过程进行了数值模拟,并对结构参数进行了优化;最后通过实验验证了计算的正确性。结果表明:当通道孔数n增大时,总热阻普遍减小;当通道单孔宽度x增大时,总热阻先增大后减小,当n=6个、x=1.670 mm时,水套具有最佳的散热性能;水套各测温点的数值模拟温度与实验测量温度之间的相对误差均低于5.00%。     

A practical perspective on plant preservation and plant life extension in thermal power stations. Considering aspects of reliability, maintainability, cost and safety

Currently I am employed as the Assistant Power Station Manager, with responsibility for all maintenance aspects, in a thermal power station which has been on standby since 1986! Previously I have been employed as a maintenance engineer and engineering manager in base loading thermal power stations where plant life extension programmes have not only been conceived and planned, but, on most occasions, even completed.

This paper reflects on aspects of plant preservation and plant life extension programmes with which I have been, and am currently, associated; weighing the obvious desirability for such programmes against the need to achieve reliability and maintainability, at a reasonable cost. (Who knows, it may even answer the question continually asked by my wife, “If you are not generating electricity, what do you do all day?”).

The paper also looks at the retention of safety standards, and the need to improve safety standards on ageing plant, in line with ever more stringent legislation.     

A weight function approach to stress-intensity factors for half-elliptical surface cracks in cylindrical pressure vessels subjected to thermal shock

Root-mean-square averaged (RMS-averaged) stress-intensity factors were calculated for internal half-elliptical surface cracks in cylindrical vessels using a weight function method. The weight function was derived based on an approximate crack surface displacement representation. Stress-intensity factors for longitudinal half-elliptical inner surface cracks subjected to polynomial stress distribution have been presented and compared favorably with the existing numerical solutions. Superposition of the polynomial stress-intensity factors has provided an extremely efficient solution to the thermal shock crack problems. The crack geometries analyzed were R_i/R₀ = 10/11 and 4/5, a/c = 0·3333 and 0·8, the ratio of crack depth to wall thickness ranged from 0 to 0·8. The results, as well as the proposed method, offer a very powerful and economic way for the safety assessment of pressure vessels subjected to complex and varying load conditions.