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Chemical engineering and industrial ecology: Remanufacturing and recycling as process systems
Full text linkClimate change and resource scarcity are just two of the planetary crises that make radical socio-economic change essential if human society is to be sustainable. Chemical engineering is a skill-set that can make a unique contribution to the socio-economic transition, going beyond new technological processes to provide a system-level understanding of economic activities from the perspective of industrial ecology. This paper provides an example by applying process system analysis to the use, re-use, remanufacturing, and recycling of material products. Unlike the ‘circular economy’ approach, the analysis starts from the stock of goods and materials in use in the economy and models the flows required to build up, operate, and maintain the stock. Metrics are developed to account for the effect of stock growth on demand for materials. The significance of the analysis is illustrated for four metals whose industrial ecologies are at different levels of maturity: lead, copper, aluminium, and lithium. Extending product life through re-use and remanufacturing is crucial for resource efficiency, using labour to reduce demand for energy and non-renewable resources. If end-of-life products are processed to recover individual elements, the cost penalties increase rapidly with the decreasing concentration of valuable materials and increasing number of materials in the mixture. Thus, shifting from a linear economy (make−use−dispose) to closed-loop use of materials involves rethinking product design to reduce the number of materials used. Material substitution to reduce demand for scarce materials needs to look beyond equivalence of function to consider changing patterns of use in the regenerative economy
"Dynamic waves in fluidized beds"
No full textPublished results on the velocity of propagation and the change of amplitude of dynamic waves in fluidized beds are reviewed and re-evaluated. A distinction is drawn between pressure waves and solids concentration waves. Over the range of frequencies of interest in fluidized beds, predictions of the velocity of compression waves by pseudo-homogeneous models and by models which treat the two phases separately differ little. Therefore the experimental results are compared against the simpler pseudo-homogeneous models. The behaviour of dynamic waves is inconsistent with models which ignore particle-particle contacts. To distinguish unambiguously between compression and dynamic waves, experiments at elevated pressure are needed. The results are not consistent with pseudo-homogeneous description of compression waves
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