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A comparison between the most promising design configurations for the industrial application of gasification based, plastics-to-energy cogenerators in the 2–6 MWe range is presented. A pilot scale bubbling fluidized bed air gasifier, having a feeding capacity of 100 kg/h, provided experimental data: the syngas complete composition, the characterization of the bed material, the entrained fines collected at the cyclone and the purge material from the scrubber. Mass and energy balances and material and substance flow analyses have been therefore drawn to assess and compare design solutions utilizing two mixed plastic wastes (MPW) obtained from separate collection of plastic packaging, after different levels of pre-treatments. The related techno-economic performances have been finally estimated on the basis of the manufacturer’s specifications. The study concludes that the MPW obtained after a very simple pre-treatment and fed to a gasifier coupled with a steam turbine is the solution that currently offers the higher reliability and provides the higher internal rate of return for the investigated range of electrical energy production.

Seven mixtures of coals, plastics and wood have been pelletized and fed into a pre-pilot scale fluidized bed gasifier in order to investigate the main aspects of the co-gasification of these materials. The main components of the obtained syngas (CO, H2, CO2, N2, CH 4, CnHm) were measured by means of on-line analyzers and a gas cromatograph. The performance of the gasifier was evaluated on the basis of syngas composition, carbon conversion efficiency, energy content of syngas, cold gas efficiency and yield of undesired by-products (tar and soot-like particulate). The results of a first series of experimental tests showed the effect of gas fluidizing velocity and that of equivalence ratio on the main performance parameters for a specific coal-plastics mixture. A second series of tests has been carried out by changing the mixture composition keeping fixed the gas velocity and equivalence ratio. The presence of wood and coal in the mixture with plastics contributed to reduce the tar production even though it is accompanied by a lower syngas specific energy. © 2009 Elsevier Ltd. All rights reserved.

Five alternative waste-derived fuels obtained from municipal solid waste and different post-consumer packaging were fed in a pilot-scale bubbling fluidized bed gasifier, having a maximum feeding capacity of 100. kg/h. The experimental runs utilized beds of natural olivine, quartz sand or dolomite, fluidized by air, and were carried out under various values of equivalence ratio. The process resulted technically feasible with all the materials tested. The olivine, a neo-silicate of Fe and Mg with an olive-green colour, has proven to be a good candidate to act as a bed catalyst for tar removal during gasification of polyolefin plastic wastes. Thanks to its catalytic activity it is possible to obtain very high fractions of hydrogen in the syngas (between 20% and 30%), even using air as the gasifying agent, i.e. in the most favourable economical conditions and with the simplest plant and reactor configuration. The catalytic activity of olivine was instead reduced or completely inhibited when waste-derived fuels from municipal solid wastes and aggregates of different post-consumer plastic packagings were fed. Anyhow, these materials have given acceptable performance, yielding a syngas of sufficient quality for energy applications after an adequate downstream cleaning. © 2010 Elsevier Ltd.

The effect of fuel composition on gasification process performance was investigated by performing mass and energy balances on a pre-pilot scale bubbling fluidized bed reactor fed with mixtures of plastic waste, wood, and coal. The fuels containing plastic waste produced less H 2 , CO, and CO 2 and more light hydrocarbons than the fuels including biomass. The lower heating value (LHV) progressively increased from 5.1 to 7.9 MJ/Nm 3 when the plastic waste fraction was moved from 0% to 100%. Higher carbonaceous fines production was associated with the fuel containing a large fraction of coal (60%), producing 87.5 g/kg Fuel compared to only 1.0 g/kg Fuel obtained during the gasification test with just plastic waste. Conversely, plastic waste gasification produced the highest tar yield, 161.9 g/kg Fuel , while woody biomass generated only 13.4 g/kg Fuel . Wood gasification showed a carbon conversion efficiency (CCE) of 0.93, while the tests with two fuels containing coal showed lowest CCE values (0.78 and 0.70, respectively). Plastic waste and wood gasification presented similar cold gas efficiency (CGE) values (0.75 and 0.76, respectively), while that obtained during the co-gasification tests varied from 0.53 to 0.73.

Gasification is a thermochemical process that aims to convert solid fuels into a synthetic gas that can be addressed to an end-use apparatus to produce electric energy and heat or can be further refined to be transformed in chemical valuable products. Many organic materials can be gasified under different operating conditions (pressure, temperature, reactants) in different kind of reactors. A technology widely utilized to gasify several solid materials is the bubbling fluidized bed reactor: this technology can ensure a very high heating rate but its performance is strongly affected by the material properties and its interaction with the bed during the process. This study aims to correlate the main process modeling outputs and experimental evidences obtained for the gasification of a commodity plastic waste, polyethylene, and a pinewood chip, to the hydrodynamics of a bubbling fluidized bed gasifier. To this end the rate controlling stage of the primary cracking stage has been determined in order to evaluate the reaction time for both the materials under typical gasification conditions and evaluate which is the characteristic time length of their primary cracking in the dense bed of the bubbling fluidized bed.

An innovative process for a mass production of multi-wall carbon nanotubes (MWCNTs) by means of pyrolysis of virgin or recycled polyolefins is described. The technique uses solid-gas fluidised bed reactors, continuously operated under conditions which allow high heating rates of the polymers, high heat and material exchange coefficients and a reliable control of residence times in the reactor. The obtained MWCNTs have been characterized by TGA, SEM and TEM microscopy as well as X-ray diffractometry and Raman spectroscopy. The results demonstrate that the proposed process allows the production of MWCNTs compatible with most of the already known applications, in large quantities and at low cost. This makes extremely wider the field of possible applications of these nanostructured materials. © 2005 Elsevier Ltd. All rights reserved.

Investigating the environmental sustainability of any recycling process demands full understanding and objective quantification of all the associated environmental impacts. Life cycle assessment is an internationally standardized method that is able to account for upstream and downstream inputs and emissions over the complete supply chain providing a product or service. It is generally considered the best environmental management tool that can be used to move from a generic statement about the environmental benefit of a given recycling or disposal system to reach an objective quantification of its environmental sustainability. In this study, it is used to assess and compare the environmental performances of three alternative options (landfilling, recycling, and combustion with energy recovery) that could be used in Italy to manage paper and board packaging waste. The results confirm that material recycling may not be the best environmental option. In this specific case, they show that paper use should be viewed in the context of the international trade in biofuels.

The paper describes the design of two mitigation systems adopted by an important food company, which uses ammonia for its refrigeration plant. The results of an accurate risk analysis identified the critical risk areas and the alternative mitigation systems. Two different approaches were used for indoor and outdoor accidents. A specific model was developed to estimate the time concentration of ammonia profile after a release inside an enclosure. It was used to minimise the amount of releasable ammonia by the insertion of automatic valve devices along the pipe containing pressurized ammonia. The approach for outdoor accidents led to the design of a fluid curtain capable of intercepting and absorbing the released ammonia cloud. Another specific model, which takes into account the two-phase character of an ammonia cloud, was devised in order to calculate the water flow rate needed to ensure adequate absorption efficiency. © 2003 Elsevier Science Ltd. All rights reserved.

The risk of defluidization during the low-temperature pyrolytic processes of polyolefins is one of the major constraints to a wider utilization of fluidized beds for the pyrolysis of plastic wastes. A predictive model can estimate the occurrence of defluidization under different operating conditions, taking into account the role of physical properties of the polymers and hydrodynamic variables of the reactor, together with that of the main operating parameters, like the process temperature and the plastic waste feed rate. The results agree well with the experimental data obtained by feeding recycled polypropylene and polyethylene in a laboratory-scale bubbling fluidized-bed pyrolyzer. An operating map allows to distinguish the region of reactor stable operation from that of defluidization.

Fluidized bed pyrolysis is a special class of feedstock recycling processes for plastics recycling which provides for a rather uniform spectrum of products, reduces the maintenance time and cost and gives the possibility to apply the process even on a relatively small scale. The present study describes investigations carried out by injecting recycled polyethylene in a laboratory scale fluidized bed reactor, batchwise or continuously operated. The batchwise experiments allowed to investigate the polymer-to-particles interactions inside the fluidized bed reactor, which strongly affect the phenomenology and the rate of polymer degradation. The continuous experiments indicated how the yield and the composition of products are affected by two key operating variables of the process: the bed temperature and the residence time in the reactor. © 2002 Elsevier Science Ltd. All rights reserved.

The combustion of cylindrical pellets of a market-available, packaging-derived fuel, obtained from a mono-material collection of polyethylene terephthalate (PET) bottles, was investigated by means of two batchwise operated bench-scale fluidized bed combustors. After devolatilization, the fixed carbon was present in the bed in three phases: an A-phase, made of aggregates of sand and char, an S-phase, made of individual carbon-covered sand particles and an F-phase, made of elutriable carbon fines, abraded by the surfaces of A- and S-phases. A simple model was developed in order to quantify the role of different phenomena affecting the overall fixed carbon conversion. The algorithm was based on a network of paths representing the generation of the three phases from the parent fuel, the crumbling of A-phase, the attrition of S-phase, the combustion of the fixed carbon as well as the elutriation of carbon fines. The calculated data compared well with the experimental results. The role of the comminution phenomena was negligible. The kinetic parameters and the bed temperature appeared to have a remarkable influence on the fixed carbon combustion efficiency. Copyright (C) 2000 Elsevier Science S.A.

Three commercially available biomass fuels, made of natural and waste wood, were fed in a pilot scale bubbling fluidized bed gasifier having an internal diameter of 0.381 m and a maximum feeding capacity of 100 kg/h. The experimental runs were carried out at about 850°C and under values of the equivalence ratio between 0.20 and 0.30. The fluidized bed was generally made of natural olivine even though some runs utilized beds of dolomite or quartz sand. Measurements taken during each run include the gas composition, the content of tar in the syngas, the mass flow rate and composition of entrained fines collected at the cyclone and the characterization of bed material. The results indicate that the air gasification process is technically feasible with all the biomass tested. The olivine as tar removal bed catalyst provides for different results with waste and natural biomass fuels.

This paper describes the utilization of the Recursive Operability Analysis for the identification of accident scenarios of a pilot plant gasifier fed with solid wastes and alternative fuels. The procedure was used for the identification of situations of potential risk during the operation of the plant and, coupled with the Fault Tree algorithm, in the successive quantification of probability of occurrence of the different potential Top Events. The results indicated that Recursive Operability Analysis can be usefully applied in the design as well as in the commissioning and in the start-up stages of the plant construction. The quantification of the actual effects of the implementation of new management criteria and design solutions can also be easily obtained. © 2007 Elsevier Ltd. All rights reserved.

Natural olivine was used as bed material during the gasification of plastic waste in a pilot-scale bubbling fluidized bed reactor. The results indicate that it works as an excellent in-situ tar reduction agent, considerably improving the quality of the gas produced, in terms of low tar content, high hydrogen volume fraction and large syngas yield. The phenomena concurring to the activation of the catalyst are described together with those that can contribute to deactivate it. A phenomenological description of the different stages occurring during gasification of plastic waste in a fluidized bed of olivine particles is also reported. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Life cycle assessment (LCA) methodology is generally considered one of the best environmental management tools that can be used to compare alternative eco-performances of recycling or disposal systems. It considers the environment as a whole, including indirect releases, energy and material consumption, emissions in the environment, and waste disposal and follows each activity from the extraction of raw materials to the return of wastes to the ground (cradle-to-grave approach). The study refers to the whole Italian system for recycling of household plastic packaging wastes. The aim was to quantify the overall environmental performances of mechanical recycling of plastic containers in Italy and to compare them with those of conventional options of landfilling or incineration and of a couple of innovative processes of feedstock recycling, low-temperature fluidized bed pyrolysis, and high-pressure hydrogenation. The results confirm that recycling scenarios are always preferable to those of nonrecycling. They also highlight the good environmental performance of new plastic waste management schemes that couple feedstock and mechanical recycling processes. © 2005 American Institute of Chemical Engineers Environ Prog, 2005

The risk of occurrence of phenomena inducing worsening of fluidisation quality and eventually leading to bed defluidisation is one of the major constraints to an easier utilisation of fluidised beds for the low-temperature pyrolysis of plastic wastes. In order to investigate these phenomena, different mixtures of plastic wastes, obtained by combination of three commercially-available recycled polymers, were fed to a laboratory-scale bubbling fluidised bed reactor. Two mechanisms of defluidisation were identified and the time at which defluidisation occurred was measured and correlated to a key variable of the process. The observed phenomenology was also simulated by means of room-temperature experiments carried out with a selected mineral oil. The results allow us to demonstrate the existence of a synergistic effect between the observed mechanisms of defluidisation. © 2004 Elsevier Ltd. All rights reserved.

Developed from chemical engineering principles and energy analysis, the life cycle assessment is an internationally standardized method that is able to account for upstream and downstream inputs and emissions related to the life cycle of a product or a service. It is generally considered the best environmental management tool that can be used to obtain an objective quantification of all the environmental impacts related with different solid waste management scenarios. In this study, it is used to assess the environmental performance of alternative solid waste management options that could be used in an area of the South of Italy suffering from a situation of weighty solid waste emergency. The extreme delicacy of the decision-making process to which the results have to contribute suggested increasing the reliability of the assessment conclusions by using a high quality of data and a deepened analysis of technical processes. An analytical comparison between three selected scenarios is reported with reference to some crucial environmental impact categories. The results quantify the relative advantages and disadvantages of different management schemes and suggest some possible improvements in design and operating criteria. © 2003 Elsevier B.V. All rights reserved.

Goal, Scope and Background. The object of the study is the Italian system of plastic packaging waste recycling, active until 2001, that collected and mechanically recycled the post-consumer PE and PET liquid containers. The phases of collection, compaction, sorting, reprocessing and refuse disposal were individually analysed and quantified in terms of energy and material consumptions as well as of emissions in the environment. The work is the result of a joint research project with the Italian Consortium for Packaging (CONAI), carried out in co-operation with the main Italian companies active in the field. The main aim was the quantification of the real advantage of plastic container recycling and the definition of criteria, at the same time environmentally compatible and economically sustainable, for their management. Main Features. For each of the unit processes, and in order to increase the data quality, all the data of interest were collected during technical visits to several selected plants active in Italy or deduced by official documents and certificate declarations of the same companies. To allow comparison of resource consumption and environmental pollution from different management scenarios producing different products, the basket of products method was applied. Results. The results indicates that the production of 1 kg of flakes of recycled PET requires a total amount of gross energy that is in the range of between 42 and 55 MJ, depending on whether the process wastes (mainly coming from sorting and reprocessing activities) were sent or not to the energy recovery. The same quantity of virgin PET requires more than 77 MJ. The energetic (and then environmental) saving is so remarkable, even for PE, being 40-49 MJ for the recycled polymer and about 80 MJ that for the virgin polyolefin. The calculations were made with the reasonable assumption that the final utilisation can use the virgin or the recycled polymer without any difference. Conclusions and Outlook. The analysis defined and verified a suitable tool in the field, based on objective data, for comparing different coherent scenarios of waste management politics. This allows one to propose the extension of the tool under different collection schemes, as well as for different systems of packaging recycling. As an immediate consequence of the success of the present study, the joint-research programme with CONAI has been extended for another three years. The focus will be the Italian system for paper and paperboard recycling and that for all plastic packagings. In parallel, a different study has been scheduled with reference to the integrated solid waste management of the Regione Campania, the largest and most populated area in the South of Italy.

The stability, in long-term operation, of fluidized bed reactors utilised to pyrolyse plastics waste can be seriously compromised by particle agglomeration phenomena. These phenomena can cause poor fluidization and eventually lead to defluidization. In order to investigate this phenomenon, a polypropylene waste from a food-packaging industry was utilised in a laboratory-scale bubbling fluidized bed reactor. The effect of the main operating variables (bed hold-up, size of inert material, fluidizing velocity, feed rate of plastic pellets) was investigated by means of experiments carried out under an inert atmosphere. The time at which defluidization occurred was correlated with some process variables by means of linear relationships. A new modelling approach was also proposed in order to predict the risk of defluidization under different operating conditions. © 2001 Elsevier Science B.V. All rights reserved.

A couple of commercially available packaging-derived fuels, both obtained as a result of mono-material recycling programs of polyethylene (PE) and polyethylene terephthalate (PET), were fed in a laboratory scale bubbling fluidized-bed reactor, made of quartz. The effect of the main operating variables (bed solids hold-up, inert material size, fluidizing velocity, plastics feed rate) on the agglomeration and the defluidization phenomena was investigated by means of experiments carried out in the bed temperature range of 450–650°C. Different mechanisms of defluidization were identified and characterized. The time at which defluidization occurred was correlated to the ratio between the bed solids hold-up and the polymer feed rate by means of linear relationships. An increase of this ratio, as well as a decrease of the bed temperature, led to a decrease of the defluidization time for both the recycled polymers. No substantial effects were found in the tested range of fluidizing gas velocities. An operating criterion to avoid defluidization was finally proposed.

A cold model of a CFB, having a 0.120m ID, 5.75m high riser, was operated at a superficial gas velocity of 6m/s and at average solids mass fluxes varying in the range between 16 and 55kg/sm2. A stream of carbon dioxide was injected continuously at a fixed position along the riser axis and used as tracer gas. Three solids, belonging to groups A and B of Geldart's classification, were selected in order to investigate separately, the effect of particle size and density on the radial mixing of the gas phase. The intensity of radial gas dispersion reduced when larger or heavier particles were used. The differences in the values of radial dispersion coefficient and Peclet number were explained, taking into account the role of the particle size with respect to the scale of gas turbulence. On a fait fonctionner un modele froid de CFB, ayant un diametre interieur de 0,120 m et une colonne montante de 5,75 m de hauteur, a une vitesse de gaz superficielle de 6 m/s et a des flux massiques de solides moyens variant entre 16 et 55 kg/cm2. Un courant de gaz carbonique a ete injecte en continu a une position le long de l'axe de la colonne montant fixe et utilise comme gaz traceur. Trois solides, appartenant aux groupes A et B de la clasification de Geldart, ont ete selectionnes pour etudier separement l'effet de la taille et de la masse volumique des particules sur le melange radial de la phase gazeuse. L'intensite de la dispersion radiale du gaz diminue avec des particules plus grosses ou plus lourdes. On explique les differences dans les valeurs du coefficient de dispersion radiale et du nombre de Peclet en tenant compte du role de la taille des particules relativement a l'echelle de la turbulence du gaz.

Cylindrical pellets of a market-available packaging-derived fuel, obtained from a mono-material collection of polyethylene terephthalate (PET) bottles, were batchwise fed to a laboratory scale circulating fluidized bed (CFB) combustor. The apparatus, whose riser was 41 mm ID and 4 m high, was operated under both inert and oxidizing conditions to establish the relative importance of purely mechanical attrition and combustion-assisted attrition in generating carbon fines. Silica sand particles of two size distributions were used as inert materials. For each run, carbon load and carbon particle size distribution in the riser and rates of attrited carbon fines escaping the combustor were determined as a function of time. A parallel investigation was carried out with a bubbling fluidized bed (BFB) combustor to point out peculiarities of attrition in CFB combustors. After devolatilization, PET pellets generated fragile aggregates of char and sand, which easily crumbled, leading to single particles, partially covered by a carbon-rich layer. The injected fixed carbon was therefore present in the bed in three phases: an A-phase, made of aggregates of sand and char, an S-phase, made of individual carbon-covered sand particles and an F-phase, made of carbon fines, abraded by the surfaces of the A- and S-phases. The effects of the size of inert material on the different forms under which fixed carbon was present in the bed and on the rate of escape of attrited carbon fines from the combustor were investigated. Features of carbon attrition in CFB and BFB combustors are discussed.

A bubbling fluidized bed reactor 102mmID has been used as pyrolyser by feeding polyethylene-terephtalate at two different reactor temperatures. Experiments were carried out with the aim to quantify the yield and composition of gas, liquids and to characterize the solid phase. The solid phase has been characterized by means of different methods: TG-DTG allowed to obtain a preliminary indication about the nature of the different compounds present in the solid sample by means of determination of the thermal stability of their structures; SEM and TEM microscopy, coupled with EDAX analysis, allowed to investigate the morphology of solid structures and to recognize the presence of some specific elements. Different nanostructures, having different degradation temperatures, have been obtained at 600°C and at 800°C. Moreover, the effect of metals extracted by reactor walls on MWCNTs production and the activation/deactivation of this "in-situ" catalyst during pyrolysis of PET is described and supported by experimental evidences.

Gasification is a thermochemical process that aims to convert solid fuels into a synthetic gas that can be addressed to an end-use apparatus to produce electric energy and heat or can be further refined to be transformed in chemical valuable products. Many solid fuels, included waste (wood, biomass, plastics, municipal solid waste, etc.), can be gasified under different operating conditions (pressure, temperature, reactants) in different kind of reactors. This paper aims to correlate the descriptive model for the gasification of a mixture of commodity plastic waste to the basic design of a bubbling fluidized bed gasifier on the basis of experimental data and mathematical calculations.

A bed of natural olivine was used during the gasification of a plastic waste in a pilot plant bubbling fluidized bed reactor. The olivine remarkably improves the quality of the product gas, in terms of low tar content, high hydrogen volume fractions and large syngas yield. It also produces a certain amount of solid carbon that deposits on bed particles and depletes their catalytic activity by saturating and masking the active sites. In order to maintain a steady- state regime and an efficient in-situ tar reduction during the gasification process a simple algorithm, based on experimental data, is proposed.

Two commercially available packaging-derived fuels (PDFs), obtained as a result of recycling programs for municipal solid wastes, were fed batchwise into two laboratory scale bubbling fluidized bed combustors. One fuel tested came from a mono-material collection of PET bottles while the other was obtained by means of a mechanical selection of plastic containers. Two experimental procedures were set up to separately investigate primary fragmentation of fuels and carbon fines generation from devolatilized particles. Results were compared with those obtained with three other waste-derived fuels, namely a refuse-derived fuel, a tyre-derived fuel and an ebonite. After devolatilization, PDF particles generated char-sand aggregates thai greatly increased the fixed carbon residence time in the fluidized bed reactors. Carbon fines generation rates, under both inert and oxidizing conditions, were much lower than those measured in the tests with other high-volatile fuels. A new descriptive model was proposed to describe the overall combustion-comminution pattern of fixed carbon during the fluidized bed combustion of the packaging-derived fuels tested. © 1998 Elsevier Science Ltd. All rights reserved.

In the family of feedstock recycling processes (the advanced recycling technologies for material recovery from plastic wastes) the fluidized bed pyrolysis is probably the most promising, for the high value of its products, the flexibility of the process and the possibility to apply it on a relatively small scale. This study describes how some process variables (bed temperature, polymer feed rate, bed hold-up, fluidizing velocity, size of inert material) affect the performance of a fluidized bed pyrolyser charged with different kind of plastic wastes. The results highlight how a deep knowledge of the hydrodynamics of the fluidized bed and of the interactions between bed and polymer particles is indispensable to define design and operating criteria for the reactor, to develop reliable modeling of its performance and to avoid economic waste.