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Post-combustion CO2 capture processes have the greatest near-term potential for reducing greenhouse gas emissions because these processes can be retrofitted to existing units, thus providing a quicker solution to mitigate CO2 environmental impacts. Among all the post-combustion technologies, adsorption processes on solid sorbents are attractive due to their low energy requirements. Great interest is focused on ultra-fine materials, whose chemico-physical properties can be tuned at the molecular level. In this framework sound-assisted fluidization has already been proved to maximize the CO2 adsorption capacity of fine sorbents with respect to common technologies, due to the higher exploitation of the exposed surface. The aim of the present work is, therefore, to compare the adsorption performances of different materials (two activated carbons, two zeolites and a metal organic framework) under sound-assisted fluidization conditions (140 dB–80 Hz) in order to maximize the gas–solid contact efficiency and, in turn, minimize the limitations to the intrinsic adsorption capacity of the sorbents. All the tests were performed at ambient temperature and pressure with values of CO2 concentration typical of flue gases (5–10 vol.%). The different behaviors exhibited by the materials were explained on the basis of their textural properties. In particular, the microporosity falling in the range of 8.3–12 A strongly affects the CO2 adsorption performances under the investigated operating conditions.

Fluidization of polydisperse mixtures of solids differing in size and/or density in a cold model CFB is studied. The attention has been focused on segregation and attrition phenomena with specific reference to conditions establishing in the primary zone of a CFB combustor. A purposely developed experimental apparatus is presented. Two bidisperse mixtures of granular solids were tested: a mixture of glass beads of different size and a mixture of silica sand and lime. Operating conditions (gas superficial velocities, solids mass fluxes) were such that hydrodynamic regimes ranging from dilute to dense bottom bed established in the riser. Segregation was assessed by periodic sampling of solids from the riser and the standpipe. Attrition by abrasion during tests carried on the sand-lime mixture was assessed by continuous collection of elutriated fines at the exhaust.

The use of a bubbling fluidized bed of inert material to improve the activated carbon performance for mercury vapor capture is explored. To this end, preliminary mercury capture experiments have been conducted in a purposely designed lab-scale pyrex reactor operated in the fluidized bed and in the entrained bed configurations. Commercial powdered activated carbon was continuously injected in the reactor and both mercury concentration and carbon elutriation rate were followed at the outlet. Transient mercury concentration profiles at the bed outlet showed that the presence of a fluidized bed led to an increase of the mercury capture efficiency and, in turn, of the activated carbon utilization. This result was explained by the larger activated carbon loading and gas/solid contact time in the reaction zone as a consequence the increased surface area available for activated carbon adhesion/deposition in the fluidized bed.

Fluidization of polydisperse mixtures of solids differing in size and/or density in a cold model CFB is studied. The attention has been focused on segregation phenomena with specific reference to conditions establishing in the primary zone of a CFB combustor. A purposely developed experimental apparatus is presented. A mixture of glass beads of different size was tested. Operating conditions (gas superficial velocities, solids mass fluxes) were such that hydrodynamic regimes ranging from dilute to dense bottom bed established in the riser. Segregation was assessed by periodic sampling of solids from the riser and the standpipe.

The paper addresses the establishment of a steady inventory of bed inert material in a fluidized bed combustor when the bed consists of fuel ash only. The analysis is based on the concept of the primary ash particle size distribution (PAPSD), defined as the PSD of primary ash particles liberated by fuel particles upon complete burn-off. An experimental procedure for the quantitative assessment of the rate of primary ash generation and of the size distribution of primary ash particles (PAPSID) is presented. The application of the procedure is demonstrated with reference to a set of solid fuels, including coals and biogenous fuels. The reliability and accuracy of the technique was satisfactorily tested, with the exception of two biomass fuels which gave rise to bed agglomeration making the application of the test procedure unsuccessful. A simplified theoretical analysis is presented, based on material balances on lumped classes of primary ash particles around the CFBC. The analysis aims at clarifying the role of the PAPSD and of the cyclone efficiency to the establishment of bed inventory, particle size distribution and solids circulation rate. Lower and upper bounds to the solids circulation rate that can be established in the steady operation of a CFBC are related to the PAPSD and to the cyclone performance.

The use of a bubbling fluidized bed of inert material to improve the activated carbon performance for mercury vapor capture is explored. To this end, mercury capture experiments have been conducted in a purposely designed lab-scale pyrex reactor operated in the fluidized bed and in the entrained bed configurations. Commercial powdered activated carbon was continuously injected in the reactor and both mercury concentration and carbon elutriation rate were followed at the outlet. Transient mercury concentration profiles at the bed outlet showed that the presence of a fluidized bed led to an increase of the mercury capture efficiency and, in turn, of the activated carbon utilization. This result was explained by the larger activated carbon loading and gas/solid contact time in the reaction zone as a consequence the increased surface area available for activated carbon adhesion/deposition in the fluidized bed.

The search of alternative to fossil fuels for both energy generation and production of organic chemicals (Chum et al. 2001) calls for usage of renewable and waste materials. In this framework, industrial wastes and residual biomass play an important role, as a possible option for substituting oil and natural gas (Consonni et al. 2009). Thermo-chemical processes can be employed for converting the wastes of interest into valuable gaseous or liquid streams. In particular, thermal gasification is the most attractive process due to multiplicity and versatility of syngas applications, such as a chemical feedstock for producing a number of chemical intermediates, a fuel by itself and an intermediate for the production of other fuels or biofuels. As concerns the fuel production, the possibility to match the producer gas output to the synthesis gas specification during the gasification process is a crucial challenge for researchers due to the significant effect that it could have on the overall process economics. In this work an experimental study of waste co-gasification with biomass was conducted using a pre-pilot plant fluidized bed gasifier in order to explore the possibility of producing a syngas with the specifications required by methanol synthesis. The bed was made of either Ni/?-alumina or pure ?-alumina particles. More specifically a series of experiments were performed to investigate the effect of bed temperature and steam-to-fuel ratio (S/F) on the outlet gas composition, while keeping fixed the equivalence ratio. The results confirm that the fluidized bed co-gasification of selected biomass and wastes (olive husk/PET and olive husk/Tyre pellets) yields a syngas composition suitable for subsequent methanol production. This is true for 0.6

Post-combustion CO2 capture strategy is one of the most advantageous approach for Carbon Capture and Storage (CCS) since it can be applied without radical changes on the plants architecture [1]. CO2 adsorption with solid sorbents is one of the most promising options for post-combustion CO2 capture. A variety of promising materials acting as CO2 physisorbent and/or chemisorbent have been reviewed [2] including activated carbons, microporous/mesoporous silica or zeolites, carbonates, polymeric resins nitrogen-functionalized, metal-organic frameworks, metal oxide, ionic liquids. Sorbent selection is a key point because the materials should be both convenient from the economic point of view and versatile over a wide range of temperature and pressures. Moreover the possibility to tolerate repeated cycles of CO2 absorption and desorption is also desirable. This work investigates the absorption behavior of CO2 of materials prepared starting from a low-cost commercial carbon black. Carbon black offers a surface prone to be modified in quite mild condition allowing both chemical functionalization and physisorption with a large array of molecules. Aim of this study is to explore the role of the surface features of the substrate in the designing competitive sorbents for CCS strategies. Three CB surface modifications were proposed, namely oxidation and functionalization with ammino-groups, coating with magnetic iron oxides (magnetite Fe3O4) and impregnation with ionic liquid (IL). A careful characterization of chemical-physical properties, including textural and morphological features of the CB-based sorbents, was performed. The ability to act as CO2 sorbents was evaluated on the basis of the breakthrough times measured in a lab-scale fixed bed set-up.

A new concept of a system for Combined Heat and Power generation is presented. The concept is based on hybrid use of two renewable energy sources, direct solar (thermodynamic solar) and biomass (indirect solar energy). Biomass combustion is conducted using a fluidized bed combustor. A second source of energy, given by the direct irradiation of the bed with a concentrated solar radiation, is integrated in the same system, using the fluidized bed as solar receiver. A Stirling engine converts heat into mechanical power. A Scheffler type mirror is adopted to allow irradiation of the system in a fixed focal point. Advantages of the proposed solution are illustrated and some preliminary results on the performance of the system, obtained with a simple model, are presented. The principal improvements with respect to existing systems of similar size and primary energy source are illustrated. The most important are the enhanced heat transfer processes that are realized with the help of the fluidized bed, and the possibility of continuous cogeneration during the day. Different working conditions are considered to estimate the contribution given by the burning of fuel, in presence as well as in absence of sun irradiation (as during the night). The distribution of energy shares among the different flux contributes is reported versus the amount of biomass burned per unit time. The results clearly demonstrate the advantage of coupling, in the same system, two sources for heat generation, thus maintaining the option of producing electricity without the supply of biomass fuel.

The effect of sulphur addition on the catalytic activity of 1%Rh/Al2O3, LaCoO3/Al2O3 and 1%Rh–LaCoO3/Al2O3 catalysts in reforming of tar produced by biomass pyrolysis has been investigated by adding 20 or 200 ppm H2S in a fixed bed reactor at 700 °C using a S-free biomass slowly pyrolyzed. The catalysts have been characterized by ICP-MS and BET analyses. The poisoning effect of sulphur has been also studied by in situ DRIFT and TPR analyses. A very high sulphur exposure of the catalysts leads to the partial inhibition of the reforming properties related to the poisoning of dispersed rhodium sites. The LaCoO3 layer effectively preserves rhodium from sulphur poisoning in the 1%Rh–LaCoO3/Al2O3, the catalyst containing both phases showing mostly unchanged catalytic properties also upon 200 ppm S-treatment under reaction conditions. The LaCoO3/Al2O3 catalyst shows reduced reforming properties coupled to an increase of cracking and total oxidation reactions associated to the partial destruction of the perovskite structure.

A major accident occurred in an Italian wool factory in 2001, culminating with a severe explosion, despite that wool is recognized as the most flame-resistant among the natural textile fibers. The analysis of this exceptional event suggests that, in addition to classical explosion parameters, three key phenomena related to the process jointly contributed to trigger the otherwise unexpected combustion of wool flock suspensions. The first and more important phenomenon is represented by the segregation of dust mixtures occurring during processing of textile fibers and storage of byproduct. Segregation may isolate and concentrate the lighter component of wool processing byproduct as a flammable dust. The main conclusion of our analysis is that, when performing risk assessment, sampling of all materials is a necessary step, since flammability and explosivity of raw materials may not be representative of the safety of the whole process. The second phenomenon is the enhancement of the combustion of the flammable dust layered on nets as they are subjected to cross-flow of air. The enhancement may be such as to promote transition from smoldering to flaming combustion of the dust layer. The third phenomenon is related to the interaction among the flame, the induced turbulence, dust dispersion into clouds and the layout of the plant. The combination of these phenomena promoted a deflagration of unexpected severity. In this paper, the dynamics of the explosion is analyzed in the light of the occurrence of the above cited phenomena. Purposely designed experimental tests have been performed to support the key role of segregation, formation, and ignition of the flammable cloud. Results clarify that real-world dust explosion accidents may be more severe than it could be anticipated on the basis of standard laboratory tests. A procedure for risk analysis is given to predict explosions of flocking materials.

Five cohesive solids have been aerated in beds activated by an acoustic field of 150 dB and 120 Hz. The solids included a catalyst, an ash, a talc and two titanium oxide pigments. Sauter particle diameters were 11, 8, 5, 0.3 and 0.16 μm for catalyst, ash, talc, TR-92 Tioxide and A-Hr Tioxide, respectively. The solids showed different particle surface geometries when observed under a scanning or a transmission electron microscope. Sound-assisted aeration gave rise to bubble-free fluidization only in the case of catalyst, ash and talc. Under these conditions, fluidization curves and bed expansion correlations were obtained. Exprimental results have been explained on the basis of a cluster-subcluster model which assumes that large clusters of particles break up into fluidizable subclusters when external (drag plus inertial) forces induced by acoustic waves overcome internal cohesive (van der Waals) forces at contact points between particles.

This paper reports the results of gasification tests using a catalytic fluidized bed gasifier to obtain a H(2)-rich stream by feeding different pellets made of wood, biomass/plastic and olive husks to the gasifier. The effects of both the steam supply and an in-bed catalyst on gasifier performance have been investigated. In general, pelletization was an effective pre-treatment for improving the homogeneity of the fuel and the reliability of the feeding devices. The use of biomass/plastic pellets in a catalyst bed yielded good results in terms of the hydrogen concentration (up to 32%vol.), even if an increase in tar production and in the fine/carbon elutriation rate was observed in comparison with wood pellets.

This work reports on a study, carried out in a lab-scale FB apparatus, on the fragmentation and attrition of two biomass fuels, wood chips and wood pellets, under gasification conditions. The aim was to highlight the possible effect of their different mechanical strength on the fuel particle size distribution and overall carbon conversion. Primary fragmentation tests were carried out by monitoring the number and size of fragments produced by each fuel particle upon FB devolatilization in nitrogen. Results showed that for wood pellets limited primary fragmentation occurred, with a fragmentation probability around 30% and particle multiplication factor of 1.4. On the contrary, wood chips were subject to extensive fragmentation as witnessed by large values of the particle multiplication factor and of the fragmentation probability. The decrease of the Sauter mean diameter upon devolatilization was caused by the combined effect of primary fragmentation and particle shrinkage. Results of char attrition experiments carried out under inert and gasification (60% inlet CO2 concentration) conditions showed that the carbon loss by elutriation is certainly one of the critical factors during the gasification process, especially for the wood chips char. The higher mechanical strength of the wood pellets appears to be somewhat beneficial for reducing carbon elutriation and for obtaining a larger carbon conversion during gasification. It was found that carbon consumption in the particles progressively weakens the char structure by pore enlargement. A gasification-assisted attrition mechanism was proposed to explain these experimental results, similar to the well known combustion-assisted attrition patterns already documented for coals under oxidizing conditions.

The present work is focused on the characterization of the aeration behaviour of two different nanopowders, Al2O3 and Fe2O3, under the application of acoustic fields of different intensities (125–150 dB) and frequencies (50–300 Hz). The two nanopowders showed slightly different behaviours; in particular, Fe2O3 is generally characterized by a better fluidization quality. These differences have been explained by referring to nanoparticles aggregates properties. In particular, aggregates size and density and fractal dimension have been numerically evaluated. The fluidization of binary mixtures of the two powders has also been investigated under the application of different acoustic fields (130–135 dB, 120 Hz) and varying the amount of the two powders from 7%wt to 90%wt of Fe2O3. The addition of Fe2O3 generally has a beneficial effect on the fluidization quality of the binary mixtures, in terms of pressure drop and bed expansion ratio, becoming relevant from an amount of Fe2O3 of 33%wt.

Fragmentation and attrition of two biomass fuels, namely wood chips and wood pellets, was investigated in a lab-scale fluidized bed apparatus under both combustion and gasification conditions. The aim was to study the effect of their different mechanical strength on fuel particle size distribution and overall carbon conversion. Primary fragmentation tests showed that for wood pellets limited fragmentation occurred during devolatilization, with a fragmentation probability around 30% and particle multiplication factor of 1.4. On the contrary, wood chips were subject to extensive fragmentation as witnessed by large values of the particle multiplication factor and of the fragmentation probability. Results of char attrition experiments carried out under inert, combustion and gasification conditions showed that the carbon loss by elutriation is only critical during gasification, especially for the wood chips char. A gasification-assisted attrition mechanism was proposed to explain the experimental results, similar to the combustion-assisted attrition already documented under oxidizing conditions. The higher mechanical strength of the wood pellets appears to be beneficial for reducing carbon elutriation and for obtaining a higher carbon conversion.

Gross solids circulation of solid phase and its influence on mixing/segregation of a large flotsam particle in beds of finer solids in unconventional fluidized beds has been investigated. A tapered two-dimensional fluidization column and a fluidization column equipped with a diverging cone as gas distributor have been adopted. The hydrodynamics of the gas-solid suspension in the two apparatus has been qualitatively assessed by visual observation and the trajectories of the centre-of-gravity of large flotsam particles have been evaluated to assess the extent of mixing/segregation.

This paper reports on a study of the attrition/fragmentation behavior of different bed materials and fuel pellets for application in fluidized bed gasification. Three different bed materials displaying catalytic activity, namely fresh and sintered dolomite and a Ni-alumina catalyst, were tested for their resistance to fragmentation and attrition in fluidized bed. The fresh dolomite displayed extensive particle breakage upon calcination and a large production of attrited fines during fluidized bed operation. The other two materials were much more resistant to attrition and appeared to be suitable for further long-term operation testing. The attrition/fragmentation resistance of three pelletized fuels, one based on wood and the other two on a mixture of wood and coal, was also characterized under both inert and gasification conditions. Pellet breakage by primary fragmentation upon devolatilization appeared to be rather limited for all fuels. On the contrary, attrition of carbon fines from the char particles during gasification was extensive, due to a gasification-assisted attrition mechanism.

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.