THE CONTINUING DEBATE OVER THE EXHAUSTION OF NONFUEL MINERAL RESOURCES

The author examines the various views of mineral scarcity, distinguishing between the physical view and the economic view of exhaustion, with the aim of clarifying where the debate stands now and why.     

Is the Intensity of Copper Use Still Declining in the USA?

This article examines several deficiencies in the standard procedure for calculating the intensity of metal use. It then investigates the possibility that the long-term decline in the intensity of copper use in the USA, which has persisted for more than four decades, has in recent years come to an end, even though the standard measures of intensity of use indicate a continuation of the downward trend, albeit at a slower rate. If true, the implications are significant for the copper industry worldwide, because the USA is the largest national market for copper. In addition, consumption trends in many other countries in some respects follow those in the USA. The results do provide some support for the hypothesis that intensity of copper use in the USA is no longer falling. They also indicate that the standard procedure significantly underestimates USA copper consumption and in turn intensity of use.     

COMBUSTION OF LOW QUALITY COALS IN FLUIDIZED BED STEAM GENERATORS

A new combustion technology has been developed in the last decade that permits the burning of low quality coal, lignite and other fuels, while maintaining stack emissions within reasonable limits. Low quality fuels can be burned directly in fluidized beds, taking advantage of low furnace temperatures and chemical activity within the bed to limit SO₂ and NO_x emissions, thereby eliminating the need for stack gas scrubbing equipment. The excellent heat transfer characteristics of the fluidized beds also result in a reduction of total heat transfer surface requirements, thus reducing the size and cost of steam generators. Tests on beds operating at pressures of one to ten atmospheres, at temperatures as high as 900°C, and with gas velocities in the vicinity of 1.30 to 4 m/s, have proven the concept. Early history of this technology is traced, and the progress that has been made in the development of fluidized bed combustion boilers, as well as work currently underway in the United States and overseas are reviewed. Details of selected fluidized bed boiler installations are presented, test results are discussed and the potential application of fluidized bed boilers in industrial plants using peat, anthracite refuse, lignite and lignite refuse is examined. Dans la demière décennie, une nouvelle technique de combustion a vu le jour, permettant de brûler du charbon de qualité inférieure, de la lignite et d'autres combustibles tout en maintenant les émanations de cheminée dans des normes raisonnables. Des combustibles de qualité inférieure peuvent être brûlés directement dans des lits liquéfiés tout en profitant des basses températures de fourneaux et des réactions chimiques dans le lit afín de limiter les émissions de bioxide de soufre (SO₂) et d'oxide nitreux (NO_x), rendant ainsi inutile tout matériel de nettoyage des émanations de cheminée. Les excellentes possibilités en matiêre de transmission de chaleur que présentent les lits liquéfiés permettent également de réduire la surface totale nécessaire au transfert de chaleur, diminuant ainsi la dimension et le coût des générateurs à vapeur. Des essais concluants ont été effectués dans des lits fonctionnant à des pressions de une à dix atmosphères, à des temperatures aussi élevées que 900°C et avec des vitesses d'émanations avoisinant 1.33 á 4 m/s. L'article fait l'historique de cette technique et considère les progrès réalisés dans la construction des chaudières utilisant le procédé de combustion des chaudières des lits liquéfiés ainsi que les travaux actuellement en cours aux Etats-Unis. L'article fournit des details sur les installations utilisant des chaudières pour lits liquéfiés, analyse les résultats des essais et examine les possibilités d'emploi de ces chaudières dans l'industrie alimentée par la tourbe, les déchets d'anthracite, la lignite et ses résidus. En la última década seha desarrollado una nueva tecnología de combustión que permite quemar carbones de bajo grado, lignitos y otros combustibles, manteniendo al mismo tiempo las emisiones de las chimeneas en niveles razonables. Carbones de bajo grado pueden ser quemados directamente en lechos fluizados aprovechando la ventaja de la baja temperature de la cámara de combustión y de la reacciones químicas en el lecho para limitar las emisiones de SO₂ y NO_x, limitando en consecuencia ia necesidad de equipo de limpieza de los gases de chimenea. Las excelentes caracter ísticas de transferencia de calor de los lechos fluizados reducen también las necesidades de superficie de transferencia de calor, lo que resulta en la disminución de costo y tamaño del sistema de generación de vapor. Este concepto queda demostrado por pruebas realized as a presiones de uno a diez atmósferas y temperatures de hasta 900°C, y velocidades de gas en la vecindad de 1.33 a 4 m/s. En este artículo se presenta el desarrollo temprano de esta tecnología, el progreso alcanzado en el desarrollo de calderos utilizando dicha tecnología y los trabajos que se están llevando a cabo en los Estados Unidos en este campo. Se discuten también detalles de instalación de calderos usando la tecnología de lechos fluidizados, las pruebas realizadas así como el potencial de su aplicación en plantas industriales que usan turba, deshechos de antracita, lignito y deshechos de lignito.     

Nested Subsets and the Distribution of Birds on Isolated Woodlots

Abstract. Distribution of bird species among isolated habitat patches (e.g., woodlots in an agricultural landscape) often appears to be nonrandom; species present in small, species-poor patches also are found in larger patches that support more species. Bird communities form 'nested subsets' (after Patterson & Atmar 1986) if all species found in small faunas also are found in more species-rich assemblages. Occurrence of a nested subset pattern implies an underlying, nonrandom pattern of species distributions. I used computer simulations to analyze the degree of nestedness exhibited by bird communities in east-central Illinois. Results demonstrated that the distribution of bird species breeding in isolated woodlots (1.8 to 600 ha) differed significantly from that predicted by a random distribution model; species assemblages were more "nested" than expected by chance. Most species present in small, species-poor woodlots also were found in larger, species-rich woodlots. As groups, species requiring forest interior habitat for breeding and species wintering in the tropics showed highly nested distributions. In contrast, short-distance migrants and species breeding in forest edge habitat showed more variable distribution patterns, species recorded on smaller woodlots were not always recorded on larger, more species-rich wood-lots. Apparent absences from larger woodlots may have reflected real distribution patterns or insufficient sampling of edge habitats. These results support previous conclusions that small habitat patches are insufficient for preservation of many species.