1,721,067 research outputs found
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 modeling of a solar receiver/thermal energy storage system based on a compartmented dense gas fluidized bed
No full textFluidized beds may be considered a promising option to collection and storage of thermal energy of solar radiation in Concentrated Solar Power (CSP) systems thanks to their excellent thermal properties in terms of bed-to-wall heat transfer coefficient and thermal diffusivity and to the possibility to operate at much higher temperature. A novel concept of solar receiver for combined heat and power (CHP) generation consisting of a compartmented dense gas fluidized bed has been proposed to effectively accomplish three complementary tasks: collection of incident solar radiation, heat transfer to the working fluid of the thermodynamic cycle and thermal energy storage. A dynamical model of the system laid the basis for optimizing collection of incident radiative power, heat transfer to the steam cycle, storage of energy as sensible heat of bed solids providing the ground for the basic design of a 700kWth demonstration CSP plant
The fate of fixed carbon during the fluidized-bed combustion of a coal and two waste-derived fuels
No full textThe fate of fixed carbon during fluidized-bed combustion of a bituminous coal and two alternative fuels. a refuse-derived fuel (RDF) and a tyre-derived fuel (TDF), was investigated. A simple model was developed based on the assumption that fixed carbon present in the bed could be lumped into a coarse particles phase and a fine carbon phase. The model is based on a network of paths representing the generation of coarse and fine char particles from the parent fuel by primary fragmentation, the fine particle production by comminution of coarse char, the combustion of the coarse and of the fine char particles, as well as the elutriation of fines. Results of computations of carbon conversion were in good agreement with those measured in batchwise experiments with each of the three fuels. Conversion of the coal takes place mainly via fuel devolatilization to coarse char which further reacts to gaseous products. Conversion of TDF occurs via the generation, upon devolatilization, of amultitude of fines which eventually undergo combustion and elutriation. The phenomenology associated with RDF fluidized-bed combustion is intermediate between those of coal and TDF. The resulting framework for the evaluation of fixed carbon balance helps in identifying key factors in the conversion of such widely different fuels. © 1996 Combustion Institute
Comminution phenomena during the fluidized bed combustion of a commercial refuse-derived fuel
No full textA commercial densified refuse-derived fuel (RDF), obtained as pellets from municipal solid wastes, was burned in two laboratory scale bubbling fluidized bed combustors, having an internal diameter of 41 mm. The apparatus were both batchwise operated at 850°C by injecting batches of RDF particles into a bed of silica sand (300-400 μm as size range) fluidized at a superficial gas velocity of 0.8 m/s. RDF particles with equivalent mean diameter ranging from 4 to 9 mm were used. Different experimental procedures were set up to separately investigate comminution phenomena of fuel particles. Results were compared with those obtained burning a South African bituminous coal. Results pointed out that RDF particles undergo a strong primary fragmentation phenomenon, with a probability of particle breakage equal to 1 for fuel particles larger than 6 mm. Attrition and char fragmentation phenomena are particularly relevant under both inert and oxidizing conditions, generating a large amount of unburned fines which may affect overall combustion efficiency
Primary and secondary fragmentation of coals in a circulating fluidized bed combustor
No full textPrimary and secondary fragmentation of two Kentucky No. 9 coals, having similar proximate and ultimate analyses but different swelling indexes (2.5 and 9, respectively), were studied in a laboratory scale circulating fluidized bed combustor (CFBC). The apparatus, having a 41-mm i.d. and 1.92-m-high riser, was operated keeping fixed the gas velocity and the size of inert bed material at values of practical interest. Two experimental procedures were used to separately investigate primary and secondary fragmentation effects taking place during fluidized bed combustion of coals. Particle multiplication factor, i.e., the number of particles generated per one mother particle, was used to quantify these effects. Statistical functions of fragmentation (the probability of breakage by primary fragmentation, the probability density that a shrinking particle of a given size breaks into fragments, and the size distribution of subparticles produced by secondary fragmentation) were also determined and embodied into an available model for circulating fluidized bed combustion of coals. On the basis of this mathematical model, the relevance of primary fragmentation on some output variables chosen to characterize the performance of a circulating fluidized bed combustor was quantified. © 1994 Combustion Institute
Reply to the letter 'Kinetics of decomposition measured using thermobalance' by Juan A. Conesa
No full textFluidized-bed combustion of a biomass char: The influence of carbon attrition and fines postcombustion on fixed carbon conversion
No full textThe fluidized-bed combustion of char from a biomass fuel (Robinia Pseudoacacia) has been studied with a focus on the fate of fixed carbon under the combined effects of coarse char combustion and attrition, of attrited carbon fines postcombustion and elutriation. Extensive postcombustion under oxidizing conditions prevents the measurement of the rates of carbon fines generation by attrition from collection of elutriated carbon. A novel technique is hereby presented to overcome this problem: the rates of coarse char attrition are evaluated from the comparison of the apparent carbon conversion rate of the actual test fuel, with that of a reference fuel, selected among those which have a negligible propensity to attrition. Results from the application of the proposed technique indicate that extensive fines generation by attrition, followed by their almost complete postcombustion, occurs during fluidized-bed combustion of Robinia char. About half of the fixed carbon burns along this pathway, the remainder being directly burnt as coarse char carbon. The occurrence of extensive attrition-postcombustion leads to enhancement of the coarse char particles' apparent Sherwood numbers by a factor of about two. Analysis of the dependence of the ratio between the fines generation rate and the parallel coarse char combustion rate on operating variables of the reactor is directed to shed light on the prevailing mechanism of carbon fines generation by attrition. It appears that, differently from low-volatile solid fuels, the percolative fragmentation mechanism plays a leading role on carbon attrition
The fate of fixed carbon during the fluidized-bed combustion of a coal and two waste-derived fuels
No full textThe fate of fixed carbon during fluidized-bed combustion of a bituminous coal and two alternative fuels. a refuse-derived fuel (RDF) and a tyre-derived fuel (TDF), was investigated. A simple model was developed based on the assumption that fixed carbon present in the bed could be lumped into a coarse particles phase and a fine carbon phase. The model is based on a network of paths representing the generation of coarse and fine char particles from the parent fuel by primary fragmentation, the fine particle production by comminution of coarse char, the combustion of the coarse and of the fine char particles, as well as the elutriation of fines. Results of computations of carbon conversion were in good agreement with those measured in batchwise experiments with each of the three fuels. Conversion of the coal takes place mainly via fuel devolatilization to coarse char which further reacts to gaseous products. Conversion of TDF occurs via the generation, upon devolatilization, of amultitude of fines which eventually undergo combustion and elutriation. The phenomenology associated with RDF fluidized-bed combustion is intermediate between those of coal and TDF. The resulting framework for the evaluation of fixed carbon balance helps in identifying key factors in the conversion of such widely different fuels. © 1996 Combustion Institute
Detection and estimation of capillary interparticle forces in the material of a fluidized bed reactor at high temperature by powder flow characterization
Full text linkTwo ceramic powder samples having different compositions of surface impurities and particle size distributions were considered. These two samples resulted from a high temperature fluidized bed reactor which in its operation showed changes of working condition that might be attributed to the onset of strong interparticle forces. The flow behaviour of these powders was characterized by the High Temperature Annular Shear Cell (HT-ASC), between ambient temperature and 500 °C. Furthermore, a model is developed to relate the change of the powder flowability to the formation of a liquid phase due to the melting of particle impurities present on the particle surface. In particular, the model is used to predict, on the base of the salt composition, the intensity of the interparticle forces at different temperatures. The interparticle forces predicted by the model can be compared with those that can be inferred from the powder flow properties measured with the HT-ASC. Therefore, it is demonstrated that it is possible to derive a theoretical model to predict interparticle forces in a particulate material relevant to fluidized bed reactor, on the basis of the impurities composition. Furthermore, it is demonstrated the possibility to correctly estimate the intensity of average interparticle forces in the same kind of material by the interpretations of bulk flow properties measured with a shear tester, even in the case in which capillary forces take the place of the much weaker van der Walls forces. More in general, the paper suggests a method by which powder rheology can be used to indirectly evaluate the effects of the interparticle forces on fluidization processes even in case in which strong capillary interaction occur
- …
