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.     

Investigation of Cu leaching from municipal solid waste incinerator bottom ash with a comprehensive approach

Municipal solid waste incinerator (MSWI) bottom ash is often reused as a secondary construction material. This study used a comprehensive approach to characterize the leaching behavior of copper (Cu) from the MSWI bottom ash. The batch titration procedure was used to determine the acid neutralizing capacity and Cu leaching as a function of pH. The sequential extraction procedure (SEP) was adopted to analyze the speciation of Cu in the MSWI bottom ash. The metal speciation equilibrium model for surface and ground water (Visual MINTEQ) was used to evaluate the equilibrium of the leachates with the relative minerals, and to determine the speciation of the aqueous Cu in the leachates. Based on the multi-analysis of the results, Cu would be significantly released from the MSWI bottom ash when it is acidic. The Cu leaching pattern was not only affected by dissolved organic carbon, it was also limited by its speciation in the MSWI bottom ash. Furthermore, almost 100% of the aqueous Cu in the leachate was bound to organic matter in basic and neutral conditions, but mostly existed as Cu²⁺ in an acidic condition. These findings provide an important insight into predicting the leaching behavior of Cu from the MSWI bottom ash, as well as its impact on the environment.     

Solar still pans— The search for inexpensive and reliable materials

The inclined-tray concept of solar-still construction involves tilting the brine-containing member of the greenhouse still parallel to the “south” pane of glass. Initiated six years ago at the University of California, the arrangement demonstrated substantial advantages with a view to the requirements for commercialization as “residential” units. Since its inception, the writer has constructed and tested approximately sixty-five different stills, in the effort to optimize service-ability, durability, and cost. The principal part of this work has been directed toward the materials system of the brine-containing member, which can be either a sheet with affixed or formed baffles, or else separate pans. This report covers materials and methods of construction, operational problems, efficiency, durability, and cost, on “pan” materials, which may be grouped as: (1) wood and wood-fiber products with coatings or impregnants, (2) thermosetting plastics, (3) thermoplastic materials, (4) asbestos-cement with impregnants and coatings, and (5) metals with coatings.

The present conclusion is that: where the product water must be entirely taste-free at the time the still is initially operated, durability of ten years or more is sought, and weight is not a significant obstacle, then porcelain enamelled steel is the material of choice. Stills of this construction are presently on the market. Meanwhile a program is underway to evaluate other materials systems, both to improve the above choice, and to make optimizations where other criteria may apply.     

New prospects in the political economy of inner-Caspian hydrocarbons and western energy corridor through Turkey

This paper makes a new conceptualization on Caspian energy system and the transit routes that pass through Turkey. Firstly, it puts forward the term of “inner-Caspian”, comprising Azerbaijan, Kazakhstan and Turkmenistan. Secondly, it identifies sub-systems of “western energy corridor through Turkey” (WECT) by diversifying: (1) “WECT inner-Caspian”, which includes hydrocarbon transportation from Azerbaijan, Kazakhstan and Turkmenistan; (2) “WECT Russia”, which is currently composed of Blue Stream gas pipeline and oil transportation by tankers through Turkish straits; and (3) “WECT Middle East”, which refers to Iranian, Iraqi and Egyptian hydrocarbons. Thirdly, this paper makes a comparative analysis on WECT systems through selected economic (reserves, supply/demand, production and transportation costs), geo-political (e.g. moves of the concerned actors), political (e.g. recent developments in government structures) and security (especially in terms of transport) indicators which bring out that “it is more reasonable for the EU to first embrace WECT inner-Caspian, then develop WECT Middle-East in order to diversify its energy supply”.     

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.     

Global oil outlook: return to the absence of surplus and its implications

As we approach the end of the 20th century, the global oil picture starts to look more like the early 1970s, which set the scene for the first oil crisis in 1973. The “security margin” — the gap between demand and production capacity, has been shrinking since the early 1990s. In 1985 OPEC was producing at only 55% of capacity. By 1997 capacity utilization had risen to 95% and, barring the full re-entry of Iraq into the oil market, capacity utilization in 1998 is projected to rise to 96% with a growth of more than 1.6 million barrels a day (mbd) in global demand. No wonder, then, that the “capacity question” has been termed “oil's perennial problem”. The dilemma confronting producers is either they face the danger of over investing if demand grows slowly or not at all, or they run the risk of investing too little, too late. Yet, without outright investment, the capacity constraint may start to bite at some point in the near future. This paper will endeavour to analyse the origins of the shrinking “security margin” and its impact on the global oil supplies, the price of oil and the global economy. It will argue that under such conditions, one has to seriously consider the possiblity of a third oil crisis capable of again disrupting the global economy, triggered again by political upheaval in the Middle East.     

A probability density function for daily insolation within the temperate storm belts

Long-term insolation data are frequently obtainable either from recordings or from various empirical formulae. Many radiation-driven processes are, however, highly non-linear. The ability to model the correct long-term frequency distribution of a sequence of radiation events having a specified long-term mean insolation, is, therefore, valuable. This paper emphasizes that the “U-shaped” cloud cover frequency distribution, characteristic of the temperate storm belts, is “mapped” into the irradiation domain in a way that augments the number of “poor” and “excellent” days of sunshine at the expense of “average” days. An analytical and adjustable model is proposed, correlating the probability density of daily clearness index with the monthly average clearness index. This model is tuned to the two longest records of solar radiation in Norway, and it is verified against independent observations from the northern temperate storm belt.     

The costs and profitability of using granulated wood ash as a forest fertilizer in drained peatland forests

Increasing and more intensive energy wood harvesting from forests necessitate efforts to ensure that adequate amounts of nutrients are recycled back onto the site. Recycling nutrients back to the forest in the form of wood ash is a natural means to correct the nutrient imbalance and acidity of forest soils that can occur from intensive management, as well as to solve the problem of disposing of wood combustion wastes. Methods of refining and spreading have been developed to improve the logistics and cost competitiveness of recycling wood ash back into the forest as fertilizer. In this study, the costs of spreading granulated wood ash in the forest were calculated under Finnish conditions. The profitability of recycling wood ash to drained peatland forests as a fertilizer was also analyzed, from the forest owner’s point of view. For this analysis, wood ash was compared with chemical fertilizer in terms of effect, cost and profitability. Wood ash fertilization using the ground-based forwarder system was two to three times cheaper than using the aerial helicopter-loader system. From the forest owner’s point of view, the fertilization of peatland forest with wood ash proved to be a very profitable silvicultural investment (IRR 3-12 percent). To improve the economics of wood ash recycling to forests, ground-based spreading of granulated ash should be emphasized. Furthermore, in order to create large enough operational units for the cost-efficient spreading of ash, there needs to be comprehensive planning of spreading sites.     

Experiences in using PRA as an operational tool

The Probabilistic Risk Assessment (PRA) of Koeberg Nuclear Power Station has been used for a number of years to support operation decision making. The principle aim of this risk assessment of Koeberg is to determine the probability of a severe accident under varying operating conditions. This plant model is used by ourselves and our licensing authority to assess nuclear safety issues. Through this process, considerable practical experience has been gained in using a “living” PRA to improve plant safety and performance. This paper presents some of the insights obtained in using reliability engineering in such a dynamic way and demonstrates that by developing and using the “living” PRA considerable safety and financial gains can be obtained. These insights mainly concern the prerequisites required before optimal use of a “living” PRA can be made. Other insights concern how PRA results are best presented and interpreted. Finally, examples are presented of occurrences when PRA was used to aid operating decisions.     

A method of testing for rating thermal storage devices based on thermal performance

This paper describes a proposed test method for determining the “effective capacity” and heat loss characteristics of thermal storage devices. The prescribed series of tests should provide useful data for the rating of thermal storage devices based on thermal performance. The apparatuses and major components used in the tests have been prescribed so a liquid or air can be used as the transfer fluid. The series of tests to be conducted consist of one steady-state test to determine the heat loss characteristics and eight transient tests to determine the “effective capacity” for both heat storage and heat removal. During the transient tests, the entering fluid temperature is changed in a step-wise manner and amount of energy either stored or removed over a specified test time is determined. Sample experimental data are given in the paper to demonstrate the concept of the transient tests.     

Strain gradient-induced diffusion of hydrogen in palladium and nickel membranes

The “uphill” diffusion of hydrogen during permeation through flat sheets of palladium and nickel has been studied by an electrochemical permeation method at 303 K. For both annealed and “as cold rolled” Pd samples, uphill diffusion effects on hydrogen absorption and desorption have been observed over a range of initial hydrogen contents from about H/Pd = 0.01, i.e. near or slightly less than the _max composition, up to H/Pd = 0.25–0.3. The occurrence of a non-Fickian component of permeation flux has been associated with temporary formation of lattice volume differences across the ( + β)/β and ( + β)/ interfaces during absorptions and desorptions, respectively. Influences of the magnitudes of galvanostatic hydrogen fluxes and of the membrane thickness on the uphill effects were examined. Analogous uphill effects were observed in similar studies with nickel membranes also in both annealed and “as cold rolled” states, which were much larger than those observed for palladium.     

About the minimum number of years required to stabilize the solar irradiation statistical estimates

Many researchers install Campbell-Stokes sunshine recorders to evaluate the global irradiation from heliophany measurements using the well-known Ångström linear regression. Because of the statistical nature of this relation, the actual solar irradiation values are determined with some given standard deviation, the fluctuation of which a poor empirical solar radiation database can contribute to. In this paper a procedure (“cross-validation”) has been devised, based on 8 years of daily sunshine and daily global solar radiation data, in order to investigate the dependence of the general standard deviation on the size of the database. Therefore one can infer that a database of at least 14 years is necessary and may be sufficient not only to obtain, by Ångström regression, a trustworthy and statistically stable estimation of the daily global solar irradiation but, further, to set up a “theoretical” and statistically stable distribution of any climatic quantity. Beyond this limit, the variability of the climatological quantities originates from only their intrinsic statistical nature, independently of the size of the database used     

Natural convection from isothermal flat surfaces

Local heat-transfer coefficients along a flat plate in natural convection in air were measured using Boelter-Schmidt type heat flux meters. Experiments were carried out for different temperature differences in heating and cooling, and with inclinations varying from the horizontal “facing upwards” position, through the vertical position, to the horizontal “facing downwards” position.

The results are presented in terms of local Nusselt number as a function of the local Grashof number “tangential component”. All runs were in the range accepted as that of laminar boundary layer flow. However, under certain conditions when the normal velocity component of the air is directed away from the surface, separated flow is indicated along the trailing part of the surface, well before turbulence sets in in the boundary layer. Separation starts at a certain point along the surface. This point is nearer to the leading edge the higher the temperature difference, and the larger the inclination of the surface to the vertical.

In a separation region, the flux density is uniform. In all other regions the results agreed closely with established theories of laminar boundary layer flow.

A leading adiabatic section, used in some of the experiments, did not affect the results. An appendix gives relations recommended for engineering calculations.     

Factors affecting the formation of lead/acid tubular positives II. Resting and extreme conditions

The first-cycle discharge capacity of tubular positive plates was determined as a function of formation conditions. “Infinite acid volumes” were us     

Ash deposition behavior under coal and wood co-firing conditions in a 300 kW downfired furnace

Growth of ash deposits when wood was co-fired with coal was visually investigated in a 300 kW pilot-scale furnace. For comparison, combustion of pure coal was also conducted. A total of 10% and 20% wood were mixed with coal. The thickness and heat flux were obtained. The collected ash deposits and fly ash were characterized by a series of analysis methods to determine the physical and mineral properties. Their relationships were also revealed. Results showed that co-firing of coal with wood dramatically increased the ash deposition propensity. During the coal combustion, shedding of ash deposit occurred and the maximum deposit thickness was 15.33 mm. A deposit thickness of up to 27.02 mm was achieved for 10% wood, and the thickness increased to 34.20 mm for 20% wood. The variation in heat flux with deposit thickness substantially changed when wood was co-fired. A significant change was also observed in the mineral composition of ash deposit with the increase in wood ratio. The proportion of anorthite increased because that of lime in fly ash increased with wood ratio. In addition, the mean diameter of fly ash particles increased as wood ratio increased.     

The influence of distance from landfill and population density on degree of wood residue recycling in Australia

Governments use numerous policy instruments to encourage both “upstream” and “downstream” sorting of residues into different recycling streams. Wood waste in particular takes up a large amount of landfill space, and its anaerobic decomposition contributes to global warming through the emission of carbon dioxide and methane. In Australia the wood residue stream, such as used pallets from the commercial and industrial sector, is of particular concern to various states and territories. Diverted wood residue can provide an important resource for use in bioenergy or biofuel production.This study attempted to identify whether there is a difference between wood separating and non-separating waste facilities. This study also attempted to determine whether there is a relationship between the amount of general (total) waste collected and variables indicating general waste generation in surrounding areas, including distance to nearest population centre, distance to nearest capital city and population “catchment” of the waste facility location.It was found that a high percentage of landfills accept wood residue (80%). The results suggest that the availability of recycling is not dependent upon the relative size of the landfill and that economies of scale are not a driving factor behind wood residue recycling opportunity, but that other factors may drive or contribute to the availability of wood residue recycling.Finally, there was no clear relationship between the amounts of general waste passing through the facilities and other variables such as distance to nearest population centres, nearest capital city and population within a given radius.     

生物质与烟煤灰的理化特性及混合灰熔融特性研究

文章利用扫描电子显微镜(SEM)、X射线荧光光谱仪(XRF)、X射线荧光衍射仪(XRD)、灰熔融特性分析仪对4种生物质(海草、梨木、榛子壳、稻秆)灰与神木烟煤灰的混合灰的熔融特性进行了研究。研究发现:水生生物质(海草)灰的掺混使混合灰的熔融特性温度先升高再降低;两种木本生物质(梨木和榛子壳)灰的掺混使混合灰的熔融特性温度逐渐升高;草本生物质(稻秆)灰的掺混对混合灰熔融特性温度的影响与水生生物质灰类似。由XRF分析可知:Na2O和CaO对于混合灰的熔融特性温度有更明显的影响,随着混合灰中Na2O含量的逐渐增加,混合灰的熔融特性温度逐渐下降;随着混合灰中CaO含量的逐渐增加,混合灰的熔融特性温度逐渐上升。由XRD结果可知:水生生物质灰在高温下容易形成熔点较低的碱金属硅酸盐,使混合灰的熔点降低;木本生物质灰中的CaCO3含量较高,能够提高混合灰的熔点;草本生物质灰与水生生物质灰类似,含有的低熔点碱金属硅铝酸盐使混合灰的熔点降低。     

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.     

Effect of wood fly ash and compost on nitrification and denitrification in agricultural soil

Wood ash from biofuel combustion plants and compost from source-separated household waste are commonly spread on forest, agricultural and horticultural soils as a valuable source of plant nutrients. However, due to anthropogenic activities, wood ash may contain high concentrations of heavy metals. Heavy metals are toxic to microorganisms and therefore, soil microbial response to wood ash should be considered when soil is amended with ash. Compost is known to improve soil structure and may also act as a bioremediating agent, mitigating any toxic effects of wood ash on soil microorganisms. In the present study, the aim was to investigate whether wood ash has any toxic effect on soil microbial activity and, if this is the case, whether compost could mitigate these effects. The effect of wood fly ash on potential ammonium oxidation rate (PAO) and potential denitrification rate (PDA) in arable soil was investigated in one dose–response assay and in two pot experiments with or without plants, respectively. The treatments were amendment with wood fly ash, compost or a combination of wood fly ash and compost. PAO and PDA were assessed immediately or after 7 and 90 days in the different experiments. Wood fly ash decreased PDA to 16–56% compared to the control, while PAO varied between 82% and 205%. Sole compost addition stimulated both processes. This positive effect was also observed in the combined wood fly ash–compost treatment. In conclusion, wood ash had a toxic effect on PDA, both on an immediate, short-term and long-term basis. Amendment of compost clearly mitigated this toxic effect. The observed toxicity could be an effect of the metal content of ash.