1,721,130 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
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
Analysis of the dynamics of heat transfer between a hot wire probe and gas fluidized beds
No full textHot wire anemometry used inside air fluidized beds of glass (175 mu m), FCC (75 mu m) and silica (85 mu m) powders (Archimedes numbers of 510, 29 and 16, respectively) allowed the measurement of the time-resolved local heat transfer coefficient. Time averages of this coefficient reproduce the same behaviour found by other authors with different experimental techniques. A stochastic model for the heat transfer rate has been developed on the basic hypothesis that heat transfer fluctuations are due to the continuous renewal of packets of solid particles along the wire. The most relevant simplifying hypothesis is that the contact time between the wire and the packet is much shorter than the characteristic heating time of the packets. With this model, probability density distributions of the heat transfer coefficient are evaluated. Comparison between experimental and theoretical results is fairly good in all experimental conditions relative to fully developed aggregative fluidization. The model is less reliable in conditions of incipient and homogeneous fluidization, where the simplifying hypotheses may not apply. Calculated values of packet to particle size ratios, lambda/d(p), are around 8 for glass, between 14 and 36 for FCC and between 17 and 32 for silica. The increasing number of particles inside a packet seems, therefore, to be correlated, on one hand, to the decreasing Archimedes number, and on the other, to an apparently reduced particle mobility of powders belonging to the Group A of the Geldart [D. Geldart, Types of gas fluidization, Powder Technol., 7 (1973) 285-292] classification. (C) 1999 Elsevier Science S.A. All rights reserved
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
Sulphur capture by limestone under periodically changing oxidising reducing conditions: the effect of the cycle time
No full textAssessment of the carbon looping (CarboLoop) concept in a novel twin fluidized bed reactor
No full textCarboLoop is an innovative method, developed and patented by Salatino and Senneca (2009, 2010) and Salatino et al. (2010), for combustion of coal with inherent separation of CO2 which represents an alternative to chemical looping combustion (CLC) for solid carbon. Unlike other CLC processes, in CarboLoop there is no need for oxygen carriers because the property of carbons to uptake oxygen at low temperatures, forming oxygenated surface complexes, and to release them as CO and CO2 at higher temperatures is exploited (Haynes, 2001). The CarboLoop concept requires the utilization of two reactors (in particular two interconnected fluidized beds): an Oxidizer, where the coal is kept in contact with air at relatively mild temperature (4400°C) to foster oxygen chemisorption, and a Desorber, operating at higher temperature (7700°C) where the oxygenated C-O compounds are desorbed in an almost pure CO2 stream. The first proof-of-concept of CarboLoop has been given by discontinuous experiments in a thermogravimetric analyzer (Salatino and Senneca, 2009, Salatino et al., 2010, Senneca et al.,2013). Experiments have been carried out using different solid carbon materials and aimed at assessing the extent and rate of oxygen uptake at different temperatures. In this study the CarboLoop concept is tested in a looping apparatus. The "Twin Bed Reactor" (Coppola et al., 2016) has been purposely developed for the characterization of looping processes at the bench scale while preserving the time-temperature history that particles experience in a real looping plant. It consists of two lab-scale bubbling beds of silica sand, acting as thermal ballast, operated batchwise, connected by a rapid solids transfer line. Carbon samples are fed to the system and undergo sequential steps of Oxidization and Desorption of pre-set duration by rapid transfer from one reactor to the other. The fuel tested is a bituminous coal char with size range of 400-1000μm. The Oxidizer was operated in air at different temperatures in the range 200-300°C with a holding time of 20 min. The desorption stage was carried out at 700-800°C with the same holding time of 20 min in N2. The progress of char oxidation was monitored following the profiles of CO and CO2 concentration in the exhaust. Moreover, the effect of multiple cycles on char oxidation/desorption propensity was investigated. Results pave the way for validation of the Carboloop concept and optimization of the process conditions
Modelling the SO2-limestone reaction under periodically changing oxidising/reducing conditions: the influence of the cycle time on reaction rate
No full textA simulation model is developed to analyse the dynamic behaviour of the SO2–limestone reaction under periodically changing
oxidizing/reducing conditions. Reference conditions assumed in the model are those typical of atmospheric )uidized-bed combustors
operated with sorbent addition. The reaction network embodies limestone calcination, lime sulphation and sulphate reduction by carbon monoxide, relevant to periodic establishment of mildly reducing atmospheres around the sorbent particle. The model applies to the early conversion of particles and for short periods of time within the sulphation time.
The influence of operating conditions on the rate of sulphur uptake by the sorbent is assessed, with particular emphasis on the effect
of the cycle time of periodic shift between oxidizing and reducing conditions. Reaction regimes corresponding to the limiting cases of
very short and very long cycle times are characterized. Analysis of model results is accomplished in the light of time-scales of circulation and periodic exposure to oxidizing=reducing conditions experienced by sorbent particles in fluidized-bed combustors
Assessment of motion-induced fluidization of dense pyroclastic gravity currents
No full textThe paper addresses some fundamental aspects of the dynamics of dense granular flows down inclines relevant
to pyroclastic density currents. A simple mechanistic framework is presented to analyze the dynamics of the
frontal zone, with a focus on the establishment of conditions that promote air entrainment at the head of the current
and motion-induced self-fluidization of the flow. The one-dimensional momentum balance on the current
along the incline is considered under the hypothesis of strongly turbulent flow and pseudo-homogeneous behaviour
of the two-phase gas-solid flow. Departures from one-dimensional flow in the frontal region are also analyzed
and provide the key to the assessment of air cross-flow and fluidization of the solids in the head of the current.
The conditions for the establishment of steady motion of pyroclastic flows down an incline, in either the
fluidized or «dry» granular states, are examined.PublishedJCR Journalope
Immobilization of Actinobacillus succinigenes in Alginate Beads for Succinic Acid Production
No full textNowadays the succinic acid (SA) - a C-4 dicarboxylic acid - is considered as one of the most promising platform chemicals produced from renewable resources via fermentation. Enhancement of the SA fermentation efficiency and productivity may take advantages from immobilized cultures.. This work reports the immobilization of Actinobacillus succinogenes cells in calcium alginate beads. Glucose was used as carbon source for the fermentation. A parallel fermentation test with free cells was carried out to assess the advantages of the immobilization technology. The immobilization in alginate beads was proved to be an effective technique for SA production by A. succinogenes. The fermentation performances of the immobilized cells were higher than those of the free cells. In particular, at initial glucose concentrations of 40 g/L the maximum productivity in immobilized cells fermentation (0.77 g/Lh) is more than twice that measured for free cells (0.32 g/Lh
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