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Gas-mixing and bed hydrodynamics associated with the rise of isolated bubbles in gas-fluidized beds of two granular solids are investigated by means of a novel technique. These diagnostics consist of an array of miniaturized zirconia-based oxygen sensors located along the axis of a hot (1123 K) incipiently fluidized bed, in which isolated bubbles of a tracer gas (nitrogen) are injected. Time-resolved oxygen concentrations and relative pressures are recorded at several levels along the bed. It is shown how the response of the sensors array can be related to the concurrent effects of bubble motion, bubble-emulsion phase, mass transfer and interstitial gas flow in the emulsion phase, combined with each other to give rise to the propagation of two perturbations to the basal value of oxygen concentration. Analysis of time-resolved oxygen concentration profiles enables the assessment of: (a) the bubble rise velocity; (b) the gas velocity associated with the interstitial flow; and (c) the interphase bubble-emulsion phase, mass-transfer rate and coefficient. Analysis of the response of sensors located in the splash zone of the fluidization column provides indirect inference of the hydrodynamic patterns associated with bubble bursting at the surface of the bed. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Il 9 gennaio 2001 un incendio ed una esplosione provocarono tre morti, sei feriti e danni ingenti ad una primaria industria laniera operante nel nord-ovest d'Italia. La sequenza degli eventi è stata analizzata sulla base degli atti processuali e di sopralluoghi sul teatro dell'incidente. Inoltre sono stati condotti test sperimentali ad hoc per contribuire a chiarire la dinamica dell'incidente e la sua eziologia. La ricostruzione dell'incidente ha mostrato che esso fu verosimilmente innescato da una iniziale stadio di combustione a brace (smoldering) di polveri deposte all'interno del reparto di stoccaggio lappole, un prodotto di scarto della manifattura laniera generata durante la cardatura usualmente considerato non infiammabile. Le fasi successive dell'incidente si sono sviluppate con modalità tipiche dell'"effetto domino" attraverso deflagrazioni multiple di polveri combustibili derivanti dal processo di lavorazione della lana, seguite da un incendio.

Processo e relativo impianto per il risanamento di reflui contenenti sostanze fenoliche mediante Pseudomonas stutzeri OX1 immobilizzato su supporto granulare in airlift

The study addresses the competition between the course of purely pyrolytic processes and heterogeneous oxidation during oxidative pyrolysis of non-conventional fuels. This feature is one key, together with volatile matter flammability and effectiveness of oxygen transport to the particle, to establish whether flaming or glowing ignition of the fuel takes place. A selection of six non conventional high volatile solid fuels is considered in the study, namely two plastics (polyethylene and polyethylene terephthalate), two lignocellulosic materials (Robinia Pseudoacacia and waste wood) and two rubber-derived materials (scrap tyres and ebonite). The analysis is based on the comparison of the behaviour of fuels when heated in a thermogravimetric apparatus under inert and oxidizing atmospheres. Further analysis is directed to assess the heterogeneous combustion kinetics of chars obtained by pre-pyrolyzing in inert conditions samples of the fuels. The study is complementary to a companion paper (Penergy Fuels 2002, 16, 653) where pyrolysis in nitrogen of the same fuels was addressed. Results indicate that heterogeneous oxidation and pyrolytic processes play different roles depending on the nature of the fuel. A general feature of all fuels tested is that burnoff cannot be simply described as sequential reaction paths corresponding to purely thermal degradation and heterogeneous oxidation. Sinergistic effects between these processes are significant and need to be taken into account.

CarboLoop 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.

The management of bed solids inventory and particle size distribution is critical to the efficient and reliable operation of fluidized bed combustors (FBC), as it affects bed hydrodynamics, heat extraction, cyclone performance, bottom vs fly ash balance, fouling, etc. The population of bed ash material establishing at steady state in a FBC is the result of concurring processes among which particle size reduction due to combustion and different modes of attrition plays a key role. A simplified theoretical framework is presented for the assessment of the inventory and particle size distribution of ash material establishing in the bed during steady operation of a fluidized bed combustor. Key properties are represented by the amount and the particle size distribution of the Primary Ash Particles (PAPs) liberated by the fuel along burn-off. The propensity of the Primary Ash Particles to undergo further secondary attrition represents another important variable in the assessment procedure. The experimental procedure for the characterization of the amount and size distribution of PAPs liberated from a solid fuel is presented. Results of the application of the procedure to a variety of fossil and biogenous fuels are reported. The impact of the PAPSD of the different fuels on the build-up of bed material during steady fluidized bed combustion is discussed. The study further addresses the assessment of the fractional ash reporting to fly ash during FB combustion of a bituminous coal and a granulated sludge. These fuels have been selected on account of the different conversion patterns they feature during burn-off: the shrinking particle/constant density conversion pattern is exhibited by bituminous coal particles; the shrinking core/constant particle size is instead the typical conversion pattern for the granulated sludge. The relative importance of the primary generation of ash material (PAPs) and of secondary attrition of PAPs is discussed in the light of the relevant conversion pattern of the parent fuel.

Limestone particles undergo different attrition/fragmentation phenomena when processed in a fluidized bed combustor: primary fragmentation (decrepitation), attrition by surface wear, attrition/fragmentation by impact loading. The present study addresses limestone attrition and fragmentation associated with impact loading, a process which may extensively occur in the jetting region of the bottom bed of fluidized bed combustors. An experimental protocol for the characterization of the susceptibility of limestones to undergo attrition/fragmentation by impact loading is reported. The application of the protocol is demonstrated with reference to an Italian limestone whose primary fragmentation and attrition by surface wear had already been characterized in previous studies. The experimental procedure is based on the characterization of the amount and particle size distribution of the debris generated upon impact of samples of sorbent particles against a target. The protocol has been applied to raw limestone as well as to calcined and spent (i.e. sulfated to exhaustion) sorbents. Measurement of particle voidage and pore size distribution by mercury intrusion was also accomplished to correlate fragmentation with the textural properties of the sorbent samples. Fragmentation by impact loading of the limestone is significant. Lime displays the largest propensity to undergo impact damage, followed by spent sorbent and raw limestone. Fragmentation of the raw limestone and of the sulphated lime follows pattern typical of the failure of brittle materials, with a clear-cut transition between chipping and fragmentation regimes. The fragmentation behaviour of lime better conforms to a ductile failure mode, with extensive generation of very fine fragments.

In this paper we present a population balance model on sorbent particles in a dual fluidized bed calcium looping process for CO2 capture. The model is based on material balances on the sorbent as it is recirculated between the calciner and the carbonator. The carbonation step is modelled by assuming a well-stirred behavior in the carbonator with a suitable expression for the rate of CO2 uptake. Sorbent regeneration is modelled under the assumption of extremely fast calcination. Sorbent attrition is also considered to account for modifications in the particle size distribution during both calcination and carbonation, using purposely-derived constitutive expressions validated against results of a parallel experimental campaign. The influence of the relevant process parameters on the degree of particle carbonation, on the CO2 capture efficiency, on the rate of sorbent elutriation, and on the thermal power demand associated with sorbent regeneration in the calciner is assessed.

The huge emission of greenhouse gases from fossil-fuelled power plants is emphasizing the need for efficient Carbon Capture and Storage (CCS) technologies. The biomimetic CO2 absorption in aqueous solutions has been recently investigated as a promising innovative alternative for post-combustion CCS. The carbonic anhydrase (CA) - a broad group of ubiquitous enzymes - may catalyse the CO2 hydration reaction and then to promote CO2 absorption rate into aqueous solutions. Nevertheless the research on this issue is quite active, the reliable designing of absorption units still requires more details. The present study proposes the design of a random packing absorption column operated with alkaline solvents supplied with CA. The height of the packed bed to fulfil the 80% of CO2 abatement from a flue gas stream was as large as 15-20 m. A comprehensive discussion of effects of operating conditions and of CA features on unit performance is reported.

The study examines the operability of a pilot plant for autothermal pyrolysis/gasification of coal from the standpoint of system hydrodynamics. The plant, owned by ENEL and located at Bastardo (Italy), consists of a circulating fluidized bed dual loop system embodying a riser as coal pyrolyser/gasifier and a second riser serving as char combustor. The system has been modelled as a combination of mutually interconnected blocks (risers, cyclones, downcomers, L-valves) after proper selection of constitutive equations for each block. The operability of the system has been theoretically investigated by mapping hydrodynamic regimes establishing in the risers of the dual loop for different sets of design variables. Results are analyzed with the aim of identifying regions in the phase space of operating variables where stable and trouble-free operation of the system can be achieved.

The study presented hereby investigates experimentally and with CFD simulations the gas distribution effect on the hydrodynamic of a Geldart Group A turbulent fluidized bed. Experiments were carried out on a cold flow fluidized bed column with an even and uneven gas distribution. Local solid volume fraction profiles were measured using optical probes at different bed heights and along two radial directions. Optical probe measurements allow catching a clear hydrodynamic difference between both even and uneven gas distributions. These results were then used to assess CFD simulations with the code Barracuda™ (MP-PIC approach). It is noteworthy that the choice of drag correlation and boundary conditions strongly influences the agreement between the experimental and CFD results. Once the correct parameters are chosen, CFD simulations captured the effect of gas distribution changes.

Carbonic anhydrase has proven to be an excellent candidate for recombinant biocatalysts production. Its ubiquitous nature and the diversity of its forms available in various microorganisms, enable the exploitation of thermophilic, psychrophilic and halophilic properties of the native enzymes. Consolidated technologies for enzyme immobilization on solid supports disclose utilization in continuous bioreactors, opening up new opportunities to use carbonic anhydrase (Russo et al., 2013; Yoshimoto and Walde, 2018). These perspectives are perfectly framed in one of the most challenging targets of modern chemical reaction engineering: developing feasible and efficient CO2 capture and utilization processes. The principles of green chemical engineering promote the use of sustainable solvents and biocatalysts by rethinking conventional processes and mining waste streams, including flue gases. For these reasons, studies focused on post-combustion CO2 capture have been increasingly directed toward using carbonic anhydrase as a biocatalyst to enhance the CO2 absorption rate in reactive absorption processes. The present contribution addresses key methodologies for carbonic anhydrase immobilization aimed to develop heterogeneous biocatalysts for CO2 capture and utilization. Advantages and drawbacks of covalent attachment on fine granular solids, immobilization into cross-linked enzyme aggregates as well as 'in vivo' immobilization methods will be addressed (Fabbricino et al., 2021). How the characterization of biocatalyst can be exploited for a CO2 capture unit design will be discussed, showing the most effective techniques (Peirce et al., 2018). Perspectives on how enzymatic reactive CO2 absorption can be applied to carbon capture and utilization will eventually be presented with a particular focus on biocatalytic CO2 fixation pathways.

Dolomite-based binders are characterised by interesting technical and environmental features. For their synthesis, sources of both CaO and MgO are required. The idea developed in this work is to couple the synthesis of dolomite-based binders, starting from a natural dolomite, through the concept of concentrated solar energy (needed to drive the endothermal dolomite calcination process) in fluidised bed reactors. To this end, a fluidised bed system, where the concentrated solar radiation is mimicked by the use of Xe-lamps (short-arc), has been set up and operated. Natural dolomite (sieved in the 420–590 μm size range) was calcined at a nominal temperature of 850 °C, and bed temperature profiles during solar-driven calcination were investigated. Then, four binders were prepared by mixing slaked dolomite (obtained from the hydration of solar calcined dolomite) with either blast furnace slag or coal fly ash as supplementary cementitious materials. The binders were hydrated for curing times ranging from 7 to 56 days. X-ray fluorescence, X-ray diffraction and combined differential thermal and thermogravimetric analyses were employed as characterisation techniques both to analyse the chemical composition of starting materials and to investigate the evolution of the hydration in the four systems.

A possibility to carry out sorption-enhanced gasification (SEG) is represented by its integration with the calcium looping concept in dual interconnected fluidized beds (DIFB). This article is focused on the sorbent CO2 uptake performance and attrition/fragmentation tendency when operating conditions simulating those of a DIFB-SEG process are adopted. Experiments were carried out on a commercial Italian limestone in a laboratory-scale DIFB reactor. Carbonation was carried out in a range of test conditions, including variable temperature (600–700°C) and absence/presence of steam (10% by volume); CO2 concentration was set at 10% by volume. The characterization is extended by investigating the behavior of preprocessed DIFB-SEG samples on impact fragmentation tests, conducted in an ex situ apparatus. Tests were carried out for impact velocities in the range 17–45 m/s. Results were discussed considering both the impact velocity value and the operating conditions under which the sample was preprocessed in the fluidized bed.

The performance of a perovskite-based oxygen carrier for the partial oxidation of methane in thermochemical energy storage applications has been investigated. A synthetic perovskite with formula La0.6Sr0.4FeO3 has been scrutinized for Chemical Looping Reforming (CLR) of CH4 under fixed-bed and fluidized-bed conditions. Temperature-programmed reduction and oxidation steps were carried out under fixed-bed conditions, together with isothermal reduction/oxidation cycles, to evaluate long-term perovskite performance. Under fluidized-bed conditions, isothermal reduction/oxidation cycles were carried out as well. Results obtained under fixed-bed and fluidized-bed conditions were compared in terms of oxygen carrier reactivity and stability. The oxygen carrier showed good reactivity and stability in the range 800–1000 °C. An overall yield of 0.6 Nm3 of syngas per kg of perovskite can be reached per cycle. The decomposition of CH4 catalyzed by the reduced oxide can also occur during the reduction step. However, deposited carbon is easily re-gasified through the Boudouard reaction, without affecting the reactivity of the material. Fluidized-bed tests showed higher conversion rates compared to fixed-bed conditions and allowed better control of CH4 decomposition, with a H2:CO ratio of around 2 and CO selectivity of around 0.8. However, particle attrition was observed and might be responsible for a loss of the inventory of up to 9%w.

A sorption-enhanced methanation concept has been recently presented, which is based on the employment of a sorbent able to capture in situ the H2O produced during the methanation reaction, in order...

The share of energy production from renewable sources is continuously increasing and aims at reaching two-thirds of primary energy supply in 2050. In this scenario, the 2009/28/EC Directive requires that at least 10% of the transportation fuel of every EU Country derives from renewable sources by 2020, thus largely encouraging the production of biofuels. The synthesis of second-generation biofuels is characterized by extensive generation of residues with large lignin content. Torrefaction can be applied to sterilize and stabilize this residue, and to upgrade its properties for subsequent utilization in the energy field. In this study, the use of solar energy via concentrating solar power systems is proposed to perform solar-assisted torrefaction of a lignin-rich residue derived from a second-generation bioethanol production plant. The process was carried out in a lab-scale directly irradiated bubbling fluidized bed (BFB) reactor, a system designed so as to simultaneously operate as a solar receiver and a reactor in real applications. Experiments were also performed in a lab-scale conventional (i.e. electrically heated) BFB test reactor. Chemical and physical analyses were performed on the product materials to investigate changes in the elemental composition and volatile matter content as a function of the reaction temperature. Heating values of the torrefied materials were also characterized. Scanning electron microscopy (SEM) analyses were performed on the torrefied residues to highlight possible differences in the structure of the materials recovered after solar and nonsolar experiments. The influence of operating conditions on the quality of the torrefied biomass has been assessed, with a particular emphasis on the possible overheating of fuel particles under the high radiative flux conditions experienced in solar-driven torrefaction.

Concentrating solar thermal (CST) technologies for power production can play a major role in the future portfolio of renewable energies. Limestone calcination/carbonation (Calcium Looping (CaL)), is an appealing reaction whose integration with CST is widely investigated for thermochemical energy storage (TCES) and carbon capture and storage/utilization (CCSU). Experimental data under realistic CST conditions/reactors currently lacks, since most of the experimental activities have been performed in thermogravimetric analyzers. In this study, CaL-CST integration was investigated in a lab-scale directly irradiated fluidized bed reactor, able to mimic the operating conditions required for industrial implementation of the technology. Three different techniques to improve the performance of CaL-CST for TCES and CCSU were investigated: i) lowering of calcination temperature; ii) precalcination; iii) use of dolomite instead of limestone. Experimental results revealed that all the strategies moderately improve system performance. After 20 cycles, depending on the technique applied, the mean carbonation degree ranges within 28.1–37.1% (TCES) and 15.3–18.7% (CCSU) with limestone, and values 61.5% (TCES) and 36.7% (CCSU) with dolomite. Figures of energy storage density are less sensitive to the different techniques, as pay for the lower calcination temperature (limestone), or for the presence of an inert MgO fraction (dolomite). Corresponding values range within 941–1065 MJ m−3 (TCES) and 777–872 MJ m−3 (CCSU), for loose-packed conditions. N2-physisorption analyses revealed that the increased reactivity arises from better microstructural properties in terms of specific surface. Optimal choice among the different strategies should consider the intrinsic peculiarities of each investigated technique.

CarboLoop is an innovative method, developed and patented by Senneca and Salatino [1], for combustion of coal with inherent separation of CO 2 which represents an alternative to chemical looping combustion (CLC) for solid carbons. 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 CO 2 at higher temperatures is exploited. 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 (200-300°C) to foster oxygen chemisorption, and a Desorber, operating at higher temperature (700-800°C) where the oxygenated C-O compounds are desorbed in an almost pure CO 2 stream. The first proof-of-concept of CarboLoop has been given by discontinuous experiments in a thermogravimetric analyzer. 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 for the first time on a bituminous char in an innovative lab-scale fluidized bed apparatus purposely developed for the characterization of looping processes. Cycles of oxidation/desorption have been carried out and CO and CO 2 concentrations have been monitored at the exhaust. Results demonstrate the capability of char to uptake oxygen at low temperature and release CO and CO 2 at higher temperature.

The loss of calcium oxide CO2 capture capacity and the extent of particle attrition over iterated cycles are relevant to the design of Calcium Looping processes. Thermogravimetric analyzers or single batch fluidized bed reactors are typically used at the lab-scale to evaluate the sorbent performance. One drawback of these devices is that they do not reproduce the thermal history that is actually experienced by sorbent particles in real looping cycles. In this study, a novel experimental device is proposed to overcome this limitation. The test reactor has been used to assess the effect of the thermal history of CaO particles on their CO2 capture capacity and attrition tendency. The results were compared to those previously obtained with the same sorbent under comparable operating conditions in a single bed apparatus. The comparison reveals that the thermal history experienced by the CaO has a non-negligible effect on its performance.

Thermochemical energy storage is gaining widespread consideration to increase energy dispatchability in concentrating solar thermal power plants. Accordingly, excess solar energy input drives an endothermic reaction, accomplishing high energy densities and virtually unlimited storage times. As gas–solid reactions are usually involved, multiphase reactor design is essential for the success of this technology. A novel concept of directly-irradiated fluidized bed autothermal reactor is investigated for applications in concentrated solar thermal technologies. The device can be operated as a rechargeable battery, alternating a charge phase, during which solar energy is collected and stored by an endothermal gas–solid reaction, and a discharge phase, during which the stored chemical energy is released by the reverse exothermic reaction. The autothermal operation, during the charge process, consists in the recovery of the sensible heat of the reaction products to preheat the reactants by means of an internal double-pipe countercurrent heat exchanger. This operation allows to increase the overall efficiency, reducing the required solar energy input. A compartmental model to simulate the operation of the thermochemical battery is developed and closed with constitutive equations and parameters obtained by previous experimental studies on lab-scale test facilities. Limestone calcination/carbonation has been considered as model reversible reaction. Both the charge and the discharge steps were assessed investigating the effect of the design and operational variables. For the charge operation, an optimal temperature was found around 900 °C with thermal efficiencies close to 90%. For the discharge operation, thermal efficiency was found to depend almost solely on the reactor temperature, reaching values as high as 80%, whereas the gas flowrate can be set independently. The upper limit for reaction temperature is set to the reaction equilibrium condition corresponding to the inlet concentration of carbon dioxide. The obtained results represent the basis for the realization of a new prototype, that will serve for the complete proof-of-concept of the directly-irradiated fluidized bed autothermal reactor.

The aim of this study is to investigate the effect of the concentration of sulphur dioxide and steam, in the flue gas subjected to CO2 capture by calcium looping, on the performance of two limestone-based sorbents. The experimental calcium looping tests were carried out in a purposely-designed Twin Bed lab-scale apparatus (consisting of two identical interconnected bubbling fluidised bed reactors), able to reproduce a realistic particle thermal/chemical/mechanical history. The two natural limestones (particle size range 0.4–0.6 mm) were selected in view of their remarkably “high” and “poor” reactivity to CO2, respectively. Calcium looping tests consisted of ten calcination/carbonation cycles (plus an eleventh calcination). Carbonation was carried out at 650 °C in an atmosphere containing 15% CO2 to simulate a typical combustion flue gas, while calcination was operated at 940 °C at 70% CO2 to simulate oxy-combustion conditions. Six different operating conditions for carbonation were tested to study the effect of SO2 and/or H2O, where steam (when present) was fed at 10%, and SO2 (when present) either at 75 ppm (a typical concentration in a pre-desulphurised combustion flue gas) or 1500 ppm (raw flue gas). The CO2 capture capacity was calculated for each carbonation stage, and the attrition rate was obtained by collection of elutriated fines from both reactors. At the end of the test, sorbent particles were further analysed for the determination of: degree of calcium sulphation, particle size distribution, porosimetric and microscopic properties. Relationships among sorbent type, operating conditions and experimental results are here discussed in detail, with the aim of originally outlining general trends arising from the comparison of the performance of the two limestones, which are characterised by very different reactivity.

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...

AMRA, Research Centre in the field of the Analysis and Monitoring of Environmental Risk, is a permanent structure for the development of innovative methodologies applied to environmental issues. In the last years, AMRA has devoted significant efforts to develop a quantitative framework for multi-risk assessment to support the identification of effective strategies, economically viable, for the mitigation of impacts due to a wide range of risk sources and their possible interactions, considering scenarios of cascading effects. AMRA has participated and led several initiatives to promote theoretical developments of multi-risk approach and to apply this approach to cases of industrial accidents triggered by natural events (Natech). In particular, various research activities have been carried out by AMRA under projects funded by the European Commission (FP6-Na.Ra.S, FP7-CRISMA, FP7-STREST). Among the recent experiences of AMRA there is also the collaboration with the Italian Ministry of Economic Development DGS-UNMIG through the ARGO project (Analysis of natural and anthropoGenic Risks of Offshore platforms). The general objective of the project is twofold: to develop methodologies to analyse natural and human-induced risks of offshore platforms; to provide technical support for the development of recommendations arising from the foregoing analysis. In particular, ARGO aims at developing and applying a multi-risk approach to the analysis of Natech events on offshore installations for hydrocarbon extraction. This paper discusses the principles of the AMRA multi-risk methodology and its applications to industrial sites. After a brief overview of the major natural phenomena that can trigger Natech events, this work focuses on the conceptual framework underpinning the multi-risk analysis applied by AMRA to the probabilistic assessment of Natech events.

The present paper addresses gas–liquid–solids hydrodynamic regimes that establish in a lab-scale internal circulation airlift operated at low superficial gas velocity batch-wise with respect to liquid and solid phases. Silica sand and glass beads have been used as bed solids at hold-up ranging between 4 and 12% by volume. Transition conditions between fixed bed, fluidized bed and solids circulation regimes have been assessed by means of analysis of pressure data, both in the time- and frequency-domains. Gas–liquid mass transfer coefficient and liquid circulation velocity have been measured in the fluidized bed and solids circulation regimes.