• Energy Research

The Ca-Looping (CaL) technology, based on a dual gas-fluidized bed system of CaO/CaCO3 particles operated at high temperature, is a viable technological process for highly efficient pre-combustion and post-combustion CO2 capture. In this paper we show a lab-scale experimental study on the carbonation/ decarbonation of a fluidized bed of CaO particles at CaL conditions as affected by the application of a high-intensity acoustic field. The results obtained demonstrate that both carbonation and decarbonation are remarkably enhanced for sound intensity levels above 140 dB and frequencies of about 100 Hz. Fine particles (of size smaller than dp 100 lm) are entrained in the oscillating gas flow induced by an acoustic field of such low frequency, which yields a strong agitation of the bed and improves the gas-solid contact efficiency. On the other hand, an intense convection of gas flow (acoustic streaming) is generated on the surface of larger particles unmovable by the sound wave, which promotes the heat/mass transfer at the gas-solid boundary in this case. Either of these mechanisms, whose relative importance will depend on the average particle size and sound frequency, will contribute to increase the carbonation and decarbonation rates of CaO fluidized beds in the CaL technology.

The paper deals with the integration between a kinematic Stirling engine and a fluidized bed combustor for micro-scale cogeneration of renewable energy. A pilot-scale facility integrating a 40 kW(t)combustor and a gamma-type Stirling engine (0.5 kW(e)) was set up and tested to demonstrate the feasibility of this solution. The Stirling engine was installed at a lateral wall of the combustor in direct contact with the fluidized bed region. An experimental campaign was executed to assess the performance of the innovative integrated system. The experimental results can be summarized in: (a) very high combustion efficiency with biomass feeding, (b) elevated heat transfer rate to the engine, (c) a relatively small share (about 2 kW(t)) transferred to the engine from the thermal power generated by the combustor (around 13 kW(t)), (d) conversion to electric power close to the upper limit of the engine, (e) limited impact of the Stirling engine on the fluidized bed behavior, for example, temperature. From the analysis of measured variables, the dynamics is dominated by the fast response of the Stirling engine, which rapidly reacts to the slow changes of the fluidized bed combustor regime: the dynamic response of the tested facility as a thermal system was slow, the time constant being of the order of 10 minutes.

Batchwise fluidized bed experiments have studied secondary fragmentation of char particles during combustion. Two chars, one from a nonswelling and the other from a swelling coal, have been tested for different particle sizes and oxygen concentrations in inlet gas. Statistical functions expressing the probability of particle fragmentation and size distribution of fragments have been determined. Model calculations show that secondary fragmentation of chars significantly influences the performance of fluidized bed combustors only if it occurs in early stage of combustion and if the fraction of particles subject to breakage is above 75%.

In this work, a yellow tuffhas been proposed for the first time as sorbent for CO2 capture. Dynamic breakthrough experiments have been performed in a fixed bed reactor at different temperatures (25-150 °C) and CO2 partial pressures (0.01-0.20 atm), focusing on the process thermodynamics and kinetics. The thermodynamic and ki- netic studies highlighted that the CO2 adsorption on the tuff in the low pressure region typical of combustion flue gases can be properly described by Freundlich's isotherm model and by the pseudo-first order kinetic model, respectively, thus indicating a physical, multilayer and heterogeneous surface binding mechanism. Based on the results obtained, it has been demonstrated that, in the framework of a real application for post- combustion CO2 capture, the natural tuff, i.e. a low-cost natural sorbent, could be more conveniently employed in vacuum swing or mixed mode in order to minimize the energy penalty of the process.

Abstract The paper deals with fluidized bed gasification of a biomass for producing a syngas with optimized hydrogen yield thanks to in-bed catalysis. Four different bed materials have been adopted: inert quartzite as reference case, olivine and dolomite as natural catalysts, and Ni-alumina as artificial catalyst. The gasification tests have been carried out at steady state in a pilot-scale bubbling fluidized bed, under operating conditions typical for gasification as reported in the paper. The gas analyses have been performed with dedicated instrumentation, like continuous analyzers and gas chromatograph, and adopting a standard protocol for tar sampling and characterization. The influence of the catalytic materials on the concentration of stable gases (e.g. H 2, CO 2 , CO, CH 4 and light hydrocarbons) as well as on the efficiency of tar conversion has been studied. In particular the artificial catalyst has the largest effectiveness in enhancing the H 2 yield as well as in tar reduction. The catalyst gives rise to an elutriation rate significantly lower than that observed for dolomite at comparable U / U mf ratio, denoting a better mechanical resistance. A stable activity of the nickel–alumina catalyst has been observed for the whole duration of reaction tests suggesting that no deactivation phenomena occurred, due to coke deposition or morphological modifications of the particles.

The different modes and sources of attrition relevant to fluidized bed combustion and gasification are surveyed. The broad spectrum of attrition mechanisms and phenomenologies is comprehensively described. The survey addresses attrition of the different types of solids employed in fluidized bed combustion and gasification: solid fuels, sorbent materials, inert bed solids (ash and ballast materials, e.g. sand). Moreover, the survey considers attrition of bed solids that are currently employed in modern solids looping processes aimed at CCS-ready conversion of solid fuels, e.g. sorbents in carbonate looping and oxygen carriers in chemical looping combustion and gasification. The analysis specifically addresses the important topic of the mutual interaction between attrition and the progress of chemical reactions. The current status of modeling of attrition phenomena and the available tools to account for attrition in comprehensive population balance models of fluidized bed combustors and gasifiers are presented. © 2013 Woodhead Publishing Limited. All rights reserved.

Currently a great emphasis is being placed on simplification and cost reduction in the production process of methanol from renewable biomass sources. The experimental results obtained in this work, using a pre-pilot fluidized bed gasifier, demonstrate that the co-gasification of regional biomass residues with PET (polyethylene terephthalate) or tyre wastes may be regarded as a useful strategy to achieve the above goals. In fact, the product gas composition resulting from the presence of the aforesaid polymeric wastes in the fuel blend is such that the gas from the steam reforming unit does not need to be further conditioned in a water-gas shift reactor; the sole carbon dioxide capture process is sufficient to meet the requirements for the downstream methanol production. No significant differences in gas composition were observed moving from the PET to tyre-based pellets, but penalties were noted for the latter concerning tar and particulate generation.

The main results, in the frame of co-gasification in fluidized bed reactor, obtained at IRC/CNR - in the last years are reported. The results confirm that co-gasification is a suitable strategy for end-life plastic waste conversion and this in turn may contribute on the reduction of plastic landfill disposal as well as to realize a plastic sustainable life cycle