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Pyrolysis of scrap tyres has been investigated by means of non-isothermal thermogravimetric analysis, at heating rates ranging from 5 to 900 degrees C/min and particle sizes of 1 and 3 mm. The occurrence of primary and secondary pyrolysis stages has been recognized at low heating rates. Based on experimental findings and on the relevant literature on pyrolysis of rubber components, a series-parallel reaction network and a kinetic model are proposed. Accordingly, the first stage of weight loss is related to depolymerization of the rubber components. The residue, upon cyclization and crosslinking, degrades in the secondary stage at larger temperatures. Kinetic parameters of primary and secondary pyrolysis and of the cyclization/crosslinking stages are determined on the basis of experimental results obtained under chemical kinetic controlled pyrolysis conditions. At large heating rates distinction between primary and secondary pyrolysis is no longer observed and a single peak of the pyrolysis rate is observed. This phenomenology can be partly related to decreasing extent of cyclization/crosslinking that take place as the heating rate is raised. Moreover, radial non-uniformities of either temperature, overall volatile pressure or concentration can be established at larger heating rates. These can be further responsible for the modification of the pyrolysis pattern. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

The 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.

The industrial processing of tomato leads to substantial amounts of residues, typically known as tomato pomace or by-products, which can represent as much as 10% by weight of fresh tomatoes. At present, these residues are either used as feedstock for animals or, in the worst case, disposed of in landfills. This represents a significant waste because tomato pomace contains high-value compounds like lycopene, a powerful antioxidant, cutin, which can be used as a starting material for biopolymers, and pectin, a gelling agent. This article presents an overview of technologies that valorize tomato by-products by recovering added-value compounds as well as generating fuel for energy production. These technologies include operations for extraction, separation, and exploitation of lycopene, cutin and pectin, as well as the processes for conversion of the solid residues to fuels. Data collected from the review has been used to develop a biorefinery scheme with the related mass flow balance, for a scenario involving the tomato supply chain of Regione Campania in Italy, using tomato by-products as feedstock.

The ability to store effectively excess of electrical energy from peaks of production is key to the development of renewable energies. Power-To-Gas, and specifically Power-To-Methane represents one of the most promising option. This works presents an innovative process layout that integrates Chemical Looping Combustion of solid fuels and a Power-to-Methane system. The core of the proposed layout is a multiple interconnected fluidized bed system (MFB) equipped with a two-stage fuel reactor (t-FR). Performances of the system were evaluated by considering a coal as fuel and CuO supported on zirconia as oxygen carrier. A kinetic scheme comprising both heterogeneous and homogeneous reactions occurring in the MFB was considered. The methanation unit was modelled developing a thermodynamic calculation method based on minimization of the free Gibbs energy. The performance of the system was evaluated by considering that the CO/CO2 stream coming from the t-FR reacts over Ni supported on alumina catalyst with a pure H2 stream generated by an array of electrolysis cells. The number of cells to be stacked in the array was evaluated by considering that a constant H2 production able to convert the whole CO/CO2 stream produced by the CLC process should be attained. The environmental performance of the proposed process was quantified using the Life Cycle Assessment (LCA) methodology. The analysis shows i) that the majority originate from the production and disposal of the oxygen carrier used in the t-FR, and ii) that reusing part of the oxygen produced by the electrolysis cells improves significantly the environmental performance of the proposed process.

Fluidization technology displays a long record of success stories, mostly related to applications to thermal and thermochemical processes, which are fostering extension to novel and relatively unexplored fields. Application of fluidized beds to collection and thermal storage of solar radiation in Concentrated Solar Power (CSP) is one of the most promising, a field which poses challenging issues and great opportunities to fluidization scientists and technologists. The potential of this growing field calls for reconsideration of some of the typical design and operation guidelines and criteria, with the goal of exploiting the inherently good thermal performances of gas-fluidized beds at their best. “Creative” and non-conventional design and operation of fluidized beds, like those based on internal and external solids circulation, may be beneficial to the enhancement of thermal diffusivity and surface-to-bed heat transfer, improving the potential for application in the very demanding context of CSP with thermal energy storage. This paper investigated: i) a fluidized bed configuration with an uneven distribution of the fluidizing gas to promote vortices in the scale of bed height (internal solids circulation); ii) a dual fluidized bed configuration characterized by an external solids circulation achieved by the operation of a riser and a bubbling fluidized bed. CFD simulations showed the hydrodynamics conditions under which the internal solids circulation was established. The hydrodynamic characterization of the external solids circulation was achieved by an experimental study carried out with different cold models. The dual fluidized bed system was optimized in terms of operating conditions and geometrical features of the connections between two fluidized beds.Fluidization technology displays a long record of success stories, mostly related to applications to thermal and thermochemical processes, which are fostering extension to novel and relatively unexplored fields. Application of fluidized beds to collection and thermal storage of solar radiation in Concentrated Solar Power (CSP) is one of the most promising, a field which poses challenging issues and great opportunities to fluidization scientists and technologists. The potential of this growing field calls for reconsideration of some of the typical design and operation guidelines and criteria, with the goal of exploiting the inherently good thermal performances of gas-fluidized beds at their best. “Creative” and non-conventional design and operation of fluidized beds, like those based on internal and external solids circulation, may be beneficial to the enhancement of thermal diffusivity and surface-to-bed heat transfer, improving the potential for application in the very demanding context of CSP with therm...

The catalytic activity in the conversion of biomass devolatilization products to syngas of a novel alumina supported Rh–LaCoO 3 catalyst has been investigated in a double fixed bed reactor system. A catalytic screening has been carried out in order to define the limits of both operation parameters and Rh load to obtain a complete tar conversion associated with the lowest coke deposition taking into account either efficiency or costs of the material. The effect of rhodium load has been investigated in the range 0.1–1 wt.%. The study of the operation parameters has been performed by modifying the reaction temperature (500–700 °C), the catalyst amount (0.25–1 g) and the N 2 flow rate (12–60 Nl h −1 ). The catalyst still provides good performances in tar and light hydrocarbons conversion when the temperature is lowered down to 600 °C. At 700 °C a complete tar conversion can be obtained both reducing the 1% Rh–LaCoO 3 catalyst amount in the reactor to 0.5 g and decreasing the Rh load down to 0.1 wt.%. TPR and DRIFT analyses have been performed to characterize the nature of Rh and to correlate this feature to the catalytic performances.

Secondary fragmentation of Kentucky No. 9 chars, obtained with two different procedures of devolatilization, has been studied in a laboratory scale circulating fluidized bed combustor. The apparatus essentially consists of a 41 mm ID, 1.92 m high riser, a solids collecting system, a 41 mm ID recirculation column. Gas velocity and size of inert material have been varied in ranges of practical interest. An appropriate experimental technique has been developed to isolate secondary fragmentation effects from those related to other comminution phenomena taking place during fluidized bed combustion of chars. Particle multiplication factor, i.e. the number of particles generated per one char particle by secondary fragmentation, has been determined for each set of experimental conditions. The probability that a shrinking particle of a given size breaks into fragments and the fragments size distribution under similarity hypothesis have also been determined. These fragmentation functions are embodied into carbon particle population balances which are the basis of circulating fluidized bed combustion modelling. © 1992 Combustion Institute.

The feasibility of adopting an oxy-combustion stage to regenerate a spent catalyst proposed for methane thermo-catalytic decomposition has been investigated in a laboratory scale bubbling fluidized bed reactor operated at 800 C and different inlet oxygen concentrations. The efficiency of carbon oxy-combustion regeneration strategy has been evaluated on the basis of the efficiency of carbon removed from the catalyst and the performance of regenerated catalyst. The effect of multiple cycles of decomposition and regeneration steps has been also quantified. Experimental activity confirmed the possibility of producing a CO2 stream that can be finalized to a sequestration unit but also indicated the requirement of a good temperature control of catalytic particles. 2009 Elsevier Inc. All rights reserved.

The present article addresses on the possibility of carrying out a two-stage operation for hydrogen production from methane Thermo-Catalytic Decomposition (TCD) in a fluidized bed, consisting into first operating the reactor for methane decomposition, until a defined catalyst deactivation degree is approached, and then operating the fluidized bed as a combustor or a gasifyer for catalyst regeneration by carbon removal. Three different strategies of catalyst regeneration, carbon combustion in air, CO2 gasification and steam gasification, have been analyzed. The regeneration strategies have been compared on the basis of the efficiency of carbon removal and the performances of regenerated catalyst with respect to the TCD process. The effect of multiple cycles of decomposition and regeneration steps has been also quantified. A reasonable cyclic process has been simulated switching between two different feeds, the first containing CH4 and the second containing air. The effect of different air regeneration times on the product distribution in the CH4 decomposition phase has been tested to individuate its optimal value.

The paper reports a preliminary study on the application of sound assisted fluidization for hot gas clean-up, with a focus on the parallel agglomeration/removal of the particulates and afterburning of residual carbon. A 41-min ID sound-assisted fluidized bed filter/afterburner has been developed and tested in experiments carried out at ambient temperature and at 850 degrees C. The application of an acoustic field of 140 dB and 120 Hz is able to increase filtration efficiency in terms of bed saturation time and removal of particulate by factors of 2 and 4, respectively. Experiments have been interpreted based on a simplified model which takes into account the role of sound in promoting the interaction between fine particles and coarse bed material. (C) 2007 Published by Elsevier B.V.

The Thermo-Catalytic Decomposition (TCD) of methane has been investigated in a laboratory scale bubbling fluidized bed reactor using a copper dispersed on γ-alumina as a catalyst. The effects of both total flow rate and amount of catalyst, i.e. contact time, as well as of reaction temperature and CH 4 inlet concentration on CH 4 to H 2 conversion, amount of carbon deposited on the catalyst and deactivation time have been investigated. The relevance of attrition phenomena have been also investigated as a useful way to mechanically regenerate the catalyst, removing the carbon deposited on the external surface of catalytic particles. Samples of bed catalytic particles after TCD tests have been characterized by means of different techniques: (i) elemental analysis to obtain the amount of carbon deposited on the catalyst; (ii) SEM/EDS analysis to determine the morphology of carbon deposited on the catalyst surface; (iii) BET analysis to obtain the surface areas of deactivated catalyst. Different dimensionless groups have been compared in order to quantitatively assess the relative importance of intrinsic kinetics and of intraparticle and interphase (bubbles to emulsion phase and emulsion phase to catalyst particle) diffusional resistances and to highlight the controlling regimes under the various operating conditions.

Cu/γ-Al 2 O 3 catalysts with different copper content prepared by wet impregnation have been studied for the thermo-catalytic decomposition (TCD) of methane in the temperature range 800–1000 °C. The materials have been characterized using ICP-MS, X-ray diffraction (XRD) and BET analysis. Their redox and catalytic behaviour has been investigated using H 2 and CH 4 temperature programmed reduction (TPR), FT-IR, TGA under reaction mixture and isothermal tests in a fixed bed reactor. The nature of the active phase and the best catalyst composition have been determined by comparison with reference compounds containing copper oxide and copper aluminate, respectively. Finally, the applicability of catalysts in a fluidized bed has been analyzed.

The catalytic combustion of methane has been investigated in a 0.10 m bubbling fluidized bed reactor with nonpremixed feedings of reactants. Copper dispersed on porous ç-Al2O3 spheres (1 mm diameter) characterized by high mechanical strength has been used as catalyst. The effect of design variables such as methane inlet concentration, bed temperature, and superficial gas velocity on methane conversion has been quantified in the ranges 4-10 vol %, 650-750 °C, and 0.40-1.30 m s-1, respectively. The propensity to attrition of the catalyst has been separately investigated under the experimental conditions tested. Results have been interpreted in the light of a simple reactor model which assumes a plug-flow pattern for the gas through the bed and mth-order catalytic kinetics with respect to fuel concentration.

Fundamental aspects of coal combustion in the two types of atmospheric fluidized combustors, i.e. those based on bubbling and on circulating technologies, have been studied in order to determine those variables which play a dominant role in the reactor performance. The analysis is based on two relatively simple models, which take into account carbon surface reaction, intraparticle and external diffusion as well as phenomena of comminution of coal and its char. Performances of the two types of fluidized-bed combustors are discussed with reference to coal combustion only, without taking into consideration the emission issues. Sensitivities of main output variables to changes in fuel properties, design and operating variables are evaluated.

Primary 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.

The multiplication of carbon particles inside the bed of a fluidised coal combustor can be related to fragmentation and attrition. Attrition generates finer carbon which is rapidly elutriated from the bed. Previous work on attrition was carried out on a non-swelling coal. The present paper reports an extension of this work to a metallurgical coke during fluidised bed combustion. In comparison with the coal, metallurgical coal is not subject to fragmentation and is less reactive. This enabled attrition to be examined separately and at higher bed carbon content for a given fluidising velocity and excess air.