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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.

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.

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.

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

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.

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.