1,721,192 research outputs found
Mixing of a Lateral Gas Stream in a Two-Dimensional Riser of a Circulating Fluidized Bed
No full textA cold model of a circulating fluidized bed having a two-dimensional riser, with a 12 x 120 mm section and a 6.4 m height, was equipped with a device to inject a lateral gas stream along the riser. The apparatus was operated under conditions ranging from those characteristic of combustors to those of gas-conversion processes. Flow structures in the interaction region between the rising gas-solids suspension and the lateral gas stream were studied by means of a motion analysis system. Three main configurations were identified. The ratio between the momentum of the lateral gas stream and that of the rising suspension was found to be the parameter able to discriminate among the three configurations. A satisfactory agreement was found with mixing data obtained using a cylindrical riser
Mixing of a Lateral Gas Stream in a Two-Dimensional Riser of a Circulating Fluidized Bed
No full textA cold model of a circulating fluidized bed having a two-dimensional riser, with a 12 x 120 mm section and a 6.4 m height, was equipped with a device to inject a lateral gas stream along the riser. The apparatus was operated under conditions ranging from those characteristic of combustors to those of gas-conversion processes. Flow structures in the interaction region between the rising gas-solids suspension and the lateral gas stream were studied by means of a motion analysis system. Three main configurations were identified. The ratio between the momentum of the lateral gas stream and that of the rising suspension was found to be the parameter able to discriminate among the three configurations. A satisfactory agreement was found with mixing data obtained using a cylindrical riser
Tar removal during the fluidized bed gasification of plastic waste
No full textA recycled polyethylene was fed in a pilot plant bubbling fluidized bed gasifier, having an internal diameter of 0.381 m and a maximum feeding capacity of 90 kg/h. The experimental runs were carried out under various operating conditions: the bed temperature was kept at about 850 °C, the equivalence ratio varied between 0.2 and 0.35, the amount of bed material was between 131 and 215 kg, the fluidizing velocity was between 0.5 and 0.7 m/s, quartz sand and olivine were used as bed material, and air and steam were used as fluidizing reactants. The results confirm that the tar removal treatments applied inside the gasifier (primary methods) can eliminate or strongly reduce the need for a further downstream cleanup of the syngas. In particular, the utilization of a natural olivine as an in situ tar reduction agent remarkably improves the quality of the product gas, in terms of both high hydrogen volumetric fraction and larger syngas yield. © 2008 Elsevier Ltd. All rights reserved
An LCA answer to the mixed plastics waste dilemma: Energy recovery or chemical recycling?
No full textThe study focuses on mixed plastics waste (MPW), whose complex and unpredictable composition (due to high polymer heterogeneity, additives, and contaminants) makes its valorisation a true technical, environmental, economic, and regulatory challenge. Chemical recycling by means of advanced thermochemical treatments (ATT) could be a successful strategy, able to support the transition from a carbon intensive to a carbon negative sector, and alternative to the current treatments of energy recovery or mechanical downcycling. Some of these ATTs provide an efficient recovery of valuable resources, such as fuels and chemicals, but their role is mainly limited by time necessary to complete the process optimization and implement the required infrastructures. A reliable identification of the best alternatives is thus crucial. A specific LCA approach quantifies the environ-mental performances of a selected set of ATT technologies for resource recovery from MPW. It includes plastics -to-energy, by combustion or gasification; plastics-to-methane and plastics-to-hydrogen, by gasification; and plastics-to-oil, by thermal pyrolysis. The results highlight the crucial role of carbon capture and storage (CCS) units, which partially reduces that of the specific thermochemical treatment. The best performances, particularly for Climate Change category, are those of the MPW-to-hydrogen by gasification, followed by those of MPW-to-energy by combustion or gasification, all equipped with CCS. The sensitivity analysis considers the evolution of the European energy mix, characterised by a larger utilisation of renewable energy sources, and highlights the corresponding increased sustainability of chemical recycling by ATTs. This suggests that the MPW dilemma should be definitively solved in a close future
How to enhance the environmental sustainability of WEEE plastics management: An LCA study
No full textA new management scheme of plastics from waste of electrical and electronic equipment (WEEE), which includes novel treatments of sorting, dissolution/precipitation, extrusion, catalytic pyrolysis, and plastic upgrading, is proposed. Its environmental performances are quantified by an attributional Life Cycle Assessment and compared with those of European currently adopted schemes, which include conventional mechanical recycling and thermal treatments as well as improper options of dumping and open burning, largely applied to WEEE plastics exported to developing countries.
The proposed innovative scheme greatly enhances the environmental sustainability of WEEE plastics management, by increasing the annual amounts of polymers sent to recycling (from 390 kt/y up to 530 kt/y), decreasing residues to be sent to combustion (from 360 kt/y up to 60 kt/y), and reducing the potential impacts of all the midpoint categories under analysis (up to 580% for that of Global Warming). These results are mainly related to the adoption of a dissolution/precipitation process, which allows recovering target polymers such as ABS, HIPS and PC, with improvements in terms of Global Warming, Non-Carcinogens, and Carcinogens equal to 246%, 69% and 35%, even when the stages of polymer upgrading and catalytic pyrolysis are not included in the analysis. The sensitivity analysis shows that advantages of the new approach substantially disappear if the awful contributions of exportation outside Europe are taken into account. This clearly indicates that the first step to
enhance the sustainability of WEEE plastics management is a strong limitation of improper treatments applied to exported wastes.A new management scheme of plastics from waste of electrical and electronic equipment (WEEE), which includes novel treatments of sorting, dissolution/precipitation, extrusion, catalytic pyrolysis, and plastic upgrading, is proposed. Its environmental performances are quantified by an attributional Life Cycle Assessment and compared with those of European currently adopted schemes, which include conventional mechanical recycling and thermal treatments as well as improper options of dumping and open burning, largely applied to WEEE plastics exported to developing countries. The proposed innovative scheme greatly enhances the environmental sustainability of WEEE plastics management, by increasing the annual amounts of polymers sent to recycling (from 390 kt/y up to 530 kt/y), decreasing residues to be sent to combustion (from 360 kt/y up to 60 kt/y), and reducing the potential impacts of all the midpoint categories under analysis (up to 580% for that of Global Warming). These results are mainly related to the adoption of a dissolution/precipitation process, which allows recovering target polymers such as ABS, HIPS and PC, with improvements in terms of Global Warming, Non-Carcinogens, and Carcinogens equal to 246%, 69% and 35%, even when the stages of polymer upgrading and catalytic pyrolysis are not included in the analysis. The sensitivity analysis shows that advantages of the new approach substantially disappear if the awful contributions of exportation outside Europe are taken into account. This clearly indicates that the first step to enhance the sustainability of WEEE plastics management is a strong limitation of improper treatments applied to exported wastes
- …
