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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.

Integration between Concentrated Solar Power (CSP) and Calcium Looping (CaL) is gaining consideration in the perspective of large shares of renewable energy sources, to smooth the variability of non-dispatchable energy input. The scope of this study is to investigate the CaL process for ThermoChemical Energy Storage (TCES), by performing a dedicated experimental campaign in fluidized bed under realistic process conditions suitable for CaL-CSP integration. Chemical deactivation of the limestone-based sorbent has been assessed by measuring the extent of Ca carbonation along iterated calcination/carbonation cycles, correlated with physico-chemical characterization of the sorbent at selected stages of the conversion. Properties that have been scrutinized were particle size distribution, bulk density, and particle size, density, and porosity of bed solids. The attainable values of energy storage density were evaluated as well. A remarkable finding of the experimental campaign is the pronounced synergistic deactivation of limestone when it is co-processed with silica sand. Chemical interaction of CaO with the silica sand constituents at the process temperatures has been scrutinized as possible responsible for the loss of reactive CaO toward CO2 uptake. Post-process of particle density data, together with N2-intrusion porosimetric analysis, and quantitative and qualitative XRD analyses, suggests that the sand/lime interaction induces a strong reduction of the total and reactive sorbent porosity and, in turn, of reactivity. Density-based classification to separate converted and unconverted limestone particles after the carbonation step has been evaluated with the goal of increasing process efficiency, by avoiding the circulation of streams with unreacted particles through the plant. For this purpose, the minimum fluidization velocity of calcined and carbonated particles has been measured after each reaction step at the relevant process temperature.

Negative-emission technologies are largely investigated to better control atmospheric carbon dioxide concentration driving global warming. Calcium looping has been proposed in literature for direct air capture, but a comprehensive system analysis is still missing. Methanation of carbon dioxide can represent an alternative to geological storage, widely investigated within the power-to-gas framework. In this study, an integrated process considering the catalytic methanation of the concentrated carbon dioxide stream after capture from ambient air by a pure hydrogen stream from water electrolysis was proposed and numerically investigated. The system relies on packed bed reactors and uses calcium oxide as sorbent, and a nickel-based catalyst for methanation. A comprehensive study on the overall system performance was carried out, assuming a carbon dioxide capture target of 100 t y−1. Model computations suggest that roughly 50-in-parallel reactors, 0.5 m diameter each, are required for a continuous operation. The overall energy demand of the integrated process ranges within 344–370 GJ tCH4−1, or 215–293 GJ tCH4−1 if neglecting the humidifier. The methanation process requires 3-in-series reactors and can yield a continuous gas stream with a flow rate of 5 kg h−1 and a methane molar fraction of nearly 91%. If this stream is exploited for heat generation, a return of energy index of 16%, or 23% if neglecting the humidifier, is foreseen. The proposed process stems as viable solution towards a circular carbon economy.

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.

Increasing the share of renewable energies and reducing the emissions of carbon dioxide are two of the major challenges of this century. Effective use of solar energy can contribute to both targets. In this study, it is investigated an integrated process in which concentrated solar power is used to perform carbon dioxide capture from a combustion power plant through the calcium looping cycle in a dual interconnected fluidized bed system. Carbon dioxide is then reacted with hydrogen obtained from water electrolysis to produce methane (power-to-gas). Electrolytic cells may be powered by photovoltaics or excess renewable energies, thus reducing their curtailment. The integrated process was studied by means of model computations. Steady state operation of the different units was considered. Intrinsic variability of the solar energy was managed with implementation of a seasonal and/or daily thermochemical energy storage strategy. Design and operational conditions assumed as a reference were those of a combustion plant of municipal solid waste located in Manfredonia (Italy). Parameters were chosen so as to reproduce realistic conditions. Model results suggest that carbon dioxide capture can range from 30% to 85%. Input thermal power of the concentrated solar power must range between 50 and 175 MWth, for 12 h of operation. A share of this energy can be integrated in the power cycle for electricity generation, upgrading the potentiality of the original combustion plant. Size of cubic storage vessels required for continuous operation of the system ranges from 10 to 70 m according to the implemented strategy. Methane yield ranges within 3–12 × 104 tons per year, and production of H2 needs a photovoltaic field of 4–5 km2 if built in Manfredonia. Altogether, the integrated plant has an overall efficiency of 20–22% and allows, simultaneously, for carbon dioxide capture, continuous integration of solar energy in the energy production cycle and carbon dioxide utilization for methane production.

The fundamental process step within the production of SNG from biomass is methane production. In the present work, methanation is considered to be carried out in a series of adiabatic fixed bed reactors with inter-cooling and product recycle. A robust mathematical model for the considered configuration has been developed that would essentially capture the fundamental operations of the methanation process and help to provide optimal guidelines for industrial operations. In detail, several CO/CO2 feed ratio compositions and recycle ratios were analyzed.

Coupling of traditional combustion technologies with solar thermal energy is fundamental to enlarge the field of applicability and to lower the costs of renewable energy sources. A possible solution is represented by direct irradiation of a flame with concentrated solar energy, so as to increase its temperature thanks to the high absorption coefficient of combustion by-products such as soot particles. In this study, we use a detailed model of soot formation and oxidation to simulate the behaviour of a coflowing diffusion ethylene flame with and without the exposure to a concentrated solar radiation. Modelling data are compared with experimental data reported in the literature. Results confirm that our model is able to reproduce the effect of radiation both matching the temperature and soot volume fraction increase. Successively, a modified version of the solar-combustion hybrid system has been setup to test the effect of solar light orientation on the combustion process. A simulator of concentrated solar energy has been used to directly irradiate the flame from the top. Thermocouple-based temperature measurements highlighted that the flame effectively absorbed solar radiation.

The path toward a greener economy is leading the world energy scenario to an ever-increasing use of renewable energy sources. Concentrating Solar Thermal (CST) systems are typically based on technologies in which solar energy, concentrated by means of optical sun tracking mirrors, is exploited to drive power cycles or sustain chemical processes. Integration of CST technologies with relatively inexpensive energy storage systems decouples the collection of solar radiation from its use, and thus greatly increases the dispatchability of thermal energy production. Huge research efforts are currently devoted to the study of ThermoChemical Energy Storage (TCES) systems, in which solar energy is used to perform endothermal chemical reactions featuring large latent heat, so as to store solar energy in the noble and stable form of chemical bonds and/or produce solar fuels. Since most TCES processes involve gas/solid chemical reactions, multiphase chemical reactors own a key role for the success of the TCES technology. In this study, a novel batch lab-scale fluidized bed reactor for TCES of concentrated solar power and solar fuels production was designed. The reactor targets at maximizing the collection of solar energy, withstanding the highly-concentrated flux typical of high-temperature CST applications and ensuring uniform temperature distribution of the reactive materials. An experimental campaign consisting in hydrodynamical and thermal characterization of the system under inert conditions was performed. Moreover, reactive tests aimed at TCES of solar energy were performed using limestone calcination/carbonation as model reversible reaction. Heating of the system was performed by means of a simulator of concentrated solar energy made of a 7 kWe short-arc Xe lamp coupled with an elliptical reflector. The hydrodynamical characterization disclosed the main features of the reactor and the possibility of establishing different regimes of operation. Thermal characterization revealed that reactor can be safely operated at temperature of over 1000 °C. Reactive tests proved the feasibility and reliability of the designed reactor toward chemical reactions aimed at TCES of concentrated solar energy and encourage future studies toward solar fuels production.

The behaviour of lignin-rich residues from a second generation bioethanol production plant has been investigated for fluidized bed combustion. The fuel has been characterized using lab-scale fluidized beds with the aid of different diagnostic and experimental protocols to investigate the devolatilization behaviour and rate, char burnout and fragmentation and attrition phenomena. The effect of bed temperature and fuel particle size onto the devolatilization rate was scrutinized, while the effect of the superficial gas velocity was studied onto the fragmentation and elutriation tendency during fluidized bed combustion experiments. A bimodal pattern in the time-resolved devolatilization rate was observed probably caused by the formation of a large-scale particle texture made of a macro-porous cortical region and of a core characterized by large voids. Devolatilization times were relatively long and increased when bed temperature was decreased. As regards fragmentation phenomena, primary fragmentation did not occur, while secondary fragmentation was active for large particles (>10 mm) at late conversion stage. Generation of fine carbonaceous particles by attrition was limited: it increased with the superficial gas velocity and it was more pronounced under inert than reactive conditions.

In this work, an innovative process layout for methane production is proposed and investigated with the aim to promote the integration of renewable energies chemical storage via hydrogen production by water electrolysis and biomass gasification. The core of the proposed layout is the integration between an experimental fluidized bed gasification system, fed with spruce wood pellets and using Fe/Al2O3 catalyst, and a conceptual methanation unit. This latter was modelled as a series of adiabatic fixed bed reactors with inter-cooling, water condensation at the exit of each reactor, and product recycle. The performance of the methanation system was evaluated by considering that the product stream coming from the gasifier system reacts, after purification and mixing with pure hydrogen coming from an electrolysis cells array, over Ni supported on alumina catalyst. The number of electrolysis cells to be stacked in the hydrogen production unit was evaluated by considering that a constant H2 production able to reach 7:1:1H2:CO:CO2 ratio at the inlet of the methanation unit should be attained.

Chemical looping combustion (CLC) is a promising carbon capture technology allowing integration with high-efficiency Brayton cycles for energy production and yielding a concentrated CO2 stream without requiring air separation units. Recently, dynamically operated fixed bed reactors have been proposed and investigated for CLC. This study deals with the technoeconomic assessment of a CLC process performed in packed beds. Following a previously published work on the topic, two different configurations are considered: one relying on a single oxygen carrier (Cu/CuO based) and the other on two in–series oxygen carriers (Cu/CuO based first, Ni/NiO based later). For both configurations, relevant process schemes are devised to obtain continuous power generation. Despite slightly larger capital costs, two-stage CLC performs better in terms of efficiency, levelized cost of electricity, and avoided CO2 costs. Fuel price and high–temperature valves costs are identified as the main variables influencing the economic performance. The use of two in–parallel packed bed reactors (2.0 m length, 0.7 m internal diameter) enables a power output of 386 kWe, a net electric efficiency of 37.2%, a levelized cost of electricity of 91 € MWhe −1, and avoided CO2 costs of 55 € tonCO2 −1 with respect to a reference pulverized coal power plant.

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.

Concentrating Solar Power (CSP) systems represent a key technology to exploit solar energy thanks to the easy integration with energy storage systems. The thermochemical energy storage (TCES) relies on reversible chemical reactions to store the solar energy in the form of chemical bonds. Limestone calcination/carbonation is an appealing reaction for TCES. This cycle has been widely studied in the Calcium Looping (CaL) process for Carbon Capture and Sequestration/Use (CCS/U), within which the calcination is usually carried out in a CO2−rich environment at temperature of 940–950 °C. When the CaL cycle is considered for TCES, the energy required by the calciner is supplied by CSP and the whole system has to work in a closed loop, as the CO2 released during the calcination is required for the subsequent carbonation. Therefore, the operating conditions resemble those typical of the CCS/U CaL. The novel idea of this work is to perform a CaL-TCES cycle working in an open loop configuration, by coupling the system with a CO2 emitting industry. Calcination can then be accomplished under air atmosphere at lower temperature, thus preserving to some extent the material reactivity. In particular, the open loop CaL-TCES cycle has been experimentally investigated using a Fluidized Bed (FB) reactor directly heated by a solar simulator (3 MW m−2 peak flux, 3 kWth total power). Several looping cycles have been carried out on a commercial limestone sample to estimate the sorbent reactivity over cycling. The properties of calcined sorbents have been investigated by chemical physical analyses. A comparison with results obtained under CCS/U CaL conditions has also been performed, to scrutinize the potential advantages of working in an open loop configuration.

Among the potential materials proposed as suitable for thermochemical heat storage, ABO3 perovskites merit significant attention for high temperature applications in concentrating solar power plants. The specific enthalpy of the reaction is a key parameter to establish the storage capacity of the system, and accordingly determines the potential impact on decreasing related costs associated with the volume of the system. Discrepancies in the referenced enthalpies may arise from different sources like the experimental sets-ups for measuring thermodynamic properties; protocols applied or the origin of the samples. This work presents a round robin test conducted by seven institutions in order to establish a standard methodology for the measurement of enthalpies of relevant thermochemical processes at high temperature. The initiative was organized within the Working Group on Thermal Storage (Activity on “Materials for Thermal Storage”) in SolarPACES Task III.Among the potential materials proposed as suitable for thermochemical heat storage, ABO3 perovskites merit significant attention for high temperature applications in concentrating solar power plants. The specific enthalpy of the reaction is a key parameter to establish the storage capacity of the system, and accordingly determines the potential impact on decreasing related costs associated with the volume of the system. Discrepancies in the referenced enthalpies may arise from different sources like the experimental sets-ups for measuring thermodynamic properties; protocols applied or the origin of the samples. This work presents a round robin test conducted by seven institutions in order to establish a standard methodology for the measurement of enthalpies of relevant thermochemical processes at high temperature. The initiative was organized within the Working Group on Thermal Storage (Activity on “Materials for Thermal Storage”) in SolarPACES Task III.

Concentrating Solar Power (CSP) systems stem out as a promising technology that has the advantage of an easy integration with thermal energy storage. The current benchmark in the CSP technology is represented by the solar tower receiver with molten salts working as heat transfer fluid. The main drawback of this system is the relatively low working temperature of the molten salts (about 565 °C), which affects the efficiency of the subsequent Rankine cycle for energy production. The use of dense suspensions of solid particles as solar receivers in CSP systems is gaining ever increasing interest, as the dense suspension can simultaneously act as receiver, heat transfer fluid and heat storage medium. Dense suspensions can work at higher temperature with respect to molten salts, even between 1000–1500 °C, without any safety, corrosion, or disposal problem. In this work, different granular materials were investigated to scrutinize their potential use as dense suspensions in directly irradiated Fluidized Bed (FB) reactors. Experimental tests were performed in a directly irradiated FB reactor exposed to a 12 kWel beam-down simulated solar furnace. The dynamics of the directly irradiated FB reactor was analyzed with specific reference to temperature distribution at the surface and in the bulk of the bed as a function of the inlet gas velocity. Material performances were compared by considering the energy required to sustain the fluidization conditions and solar absorption capacity of the granular material.

Concentrating solar power (CSP) technologies with energy storage can greatly enhance the dispatchability and the exploitation of solar energy in different applications. In this context, the present study addresses coupling CSP with calcium looping (CaL) along the 2-fold perspective of accomplishing: (a) carbon capture and sequestration or utilization (CCSU); (b) thermochemical energy storage (TCES). The experimental campaign, aimed at assessing limestone performances over extended cycling under realistic operating conditions, was performed in a fluidized bed reactor directly irradiated by a simulator of concentrated solar radiation. Infrared thermography was used to map the fluidized bed surface during “solar-driven” calcination. Experimental results indicated that TCES operating conditions yield a more reactive material due to the development of better microstructural properties, as inferred from N2- and Hg-intrusion porosimetry, which reflect the different thermal history experienced by sorbent material. Working out of process variables in terms of density of energy storage revealed that the CSP-CaL integrated process can represent an attractive alternative option to commercial technologies based on molten salts.

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.

Carbon Capture and Sequestration (CCS) and renewable energy sources are both essential to mitigate the CO2 emissions in the near future. Calcium Looping (CaL) is an important post-combustion carbon capture technology that has reached the maturity of the pilot plant stage. On the other side Concentrated Solar Power (CSP) is a fast-growing renewable technology in which solar energy, concentrated up to several MW m−2, can be used to produce electricity or to drive an endothermic chemical reaction. The integration between a CSP system and a CaL cycle, in order to use a renewable source to supply the energy required by the calciner, would strongly improve the performance of the CaL process by overcoming some of its main drawbacks. However, the role that highly concentrated radiation can have on the sorbent properties in the CaL cycle is still matter of investigation. In this study, the CaL-CSP integrated process is experimentally investigated through the use of a directly irradiated Fluidized Bed (FB) reactor. Simulated concentrated solar radiation featured a peak flux on the FB surface of approximately 3 MW m−2 and a total power of about 3 kWth. Several calcination and carbonation tests have been performed on samples of a commercial Italian limestone, in order to establish the evolution of the sorbent capacity of CO2 capture at increasing number of cycles. The properties of the limestone samples were further investigated by means of microstructural characterization. The comparison between results obtained with and without the use of the solar concentrated flux to thermally sustain calcination provides useful information on the potential of solar driven CaL and on the measure to overcome some of its potential limitations.

Cement production is an energy-intensive manufacturing process with potentially large environmental burdens. Among the others, it is one of the largest industrial sources of CO2 emission. Limestone calcination is the stage responsible for most of CO2 emissions and energy requirement. This article aims at supporting the use of solar energy as non-carbogenic renewable source to sustain limestone calcination, with advantages on both the economic and environmental aspects of the process. A directly irradiated Fluidised Bed (FB) reactor was used as limestone precalciner for clinker production. Concentrated solar radiation was simulated with an array of three short-arc Xe-lamps of 4 kWel each, coupled with elliptical reflectors, capable of producing a peak flux of about 3 MW m−2 at the centre of the reactor. The total irradiated power is of approximately 3.2 kWth. Thermocouples and an IR camera were used for the analysis of the FB thermal profiles. Calcination was carried out at a nominal bulk bed temperature of 950 °C, in an atmosphere containing about 70% CO2. The reactivity of lime generated by the solar-driven calcination process has been characterised. Lime produced by the solar-driven process was used together with commercial clay as kiln feed components for the formulation of Portland cement samples. A binary mixture composed by fresh limestone and the same clay as above was employed as a reference. The key focus of the investigation was the assessment of the reactivity of the solar-generated lime toward the main clay components in the clinker production process, as compared to lime from ordinary calcination. An aspect that is specifically scrutinised is whether the different, and possibly more severe, thermal history to which limestone particles undergo during solar-driven calcination in directly irradiated FB reactors may compromise lime reactivity. Portland clinkers were produced by burning the raw meals at 1500 °C for 15 min. Clinkers were mixed with 5% natural gypsum to prepare the related Portland cements, which were then paste hydrated for times ranging from 2 to 28 days (water/cement mass ratio = 0.5, 20 °C, 95% relative humidity). Parameters as lime saturation factor, burnability, phase composition of clinkers and hydration behaviour of cement pastes were taken into consideration. Techniques as X-ray fluorescence and diffraction, and simultaneous differential thermal–thermogravimetry were used to study the materials.

A mathematical model of a rotary kiln oxy-pyrolyser of sewage sludge is presented. The specific feature of the model is the consideration of the effect of axial staging of oxygen feeding to the reactor as one important key to the quality and productivity of the syngas, with a focus on the fate of tar and generation of soot. The gaseous oxidiser is fed to the reactor at multiple locations along its axis in a way that reproduces the paradigm of the Zwietering reactor. The fate of gaseous components and tar is followed using a simplified lumped-kinetic mechanism that was purposely developed. The model implements submodels for heat transfer among the phases and with the wall which embody radiative, convective and conductive terms. Homogeneous reactions in gas phase are modelled with a kinetic submodel that considers the generation of primary tars from devolatilisation of fuel and subsequent formation of secondary tars and soot by thermal cracking. The model validity has been confirmed by critical comparison with experimental literature data referring to a similar case. The steady operation of the oxy-pyrolyser is analysed in terms of fluxes of solid fuel and gaseous species, extent of fuel devolatilisation, temperature profiles of solid and gas phases along the reactor. The performance of the reactor is characterised in terms of process rate and chemical composition of the produced syngas, along with its heating value and thermal power. The influence of the distributed feeding is assessed by comparison with a benchmark case consisting of conventional non-distributed feeding.

Directly irradiated fluidized bed reactors are very promising in the context of concentrated solar power applications, as they can be operated at process temperatures high enough to perform thermochemical storage reactions with high energy density. Limestone calcination-carbonation is an appealing reaction for thermochemical storage applications due to the cheapness of the raw material, and the interesting value of the reaction enthalpy at fairly high process temperatures. Moreover, limestone calcination-carbonation is intensively studied in Calcium Looping (CaL) application for post combustion CO2 capture and sequestration. In this work, the dynamics of a directly irradiated 0.1 m ID fluidized bed reactor exposed to a 12 kWel simulated solar furnace is analyzed with specific reference to temperature distribution at the surface and in the bulk of the bed. Simulation of the solar radiation was performed through an array of three short arc Xe-lamps coupled with elliptical reflectors, yielding a peak flux of nearly 3000 kW m-2 and a total power of nearly 3 kW incident on the bed surface. Moreover, the directly irradiated fluidized bed reactor has been used to perform CaL tests by alternating solar-driven limestone calcination and autothermal recarbonation of lime. CaL has been investigated with the twofold perspective of: a) accomplishing energy storage by solar-driven calcination of limestone; b) perform solar-aided CO2 capture from flue gas to be embodied in carbon capture and sequestration schemes.

Calcium Looping (CaL) is a promising post-combustion CO2 capture and storage technique. Thermal input to the calciner, which is needed to sustain the endothermicity of sorbent regeneration, is usually accomplished via oxy-combustion of an auxiliary fuel. The idea behind the present study is to couple CaL with a Concentrated Solar Power (CSP) system, so that all the thermal energy required in the calciner is supplied by a renewable source. The integration of a CaL cycle with a CSP system offers several potential technical, economical and environmental advantages, but must cope with the inherently unsteady nature of incident solar power. The cyclic character of incident solar power as compared with steady CaL operation could be managed in different ways. In the present study a simple scheme of integrated CaL-CSP process is suggested, based on storage of the excess incident power during the daytime as calcined sorbent, which is eventually utilized in the CaL loop during the nighttime. A preliminary assessment of the performance of this integrated scheme is accomplished by means of model computations. The model is based on a population balance model on sorbent particles, which takes into account the cyclic operation of the system. The parameters of the solar field and the influence of the main operating parameters (sorbent residence time, sorbent/CO2 inlet molar ratio, fluidization velocity) on carbonation degree and efficiency, on sorbent loss by elutriation, on thermal power demand at the calciner and on thermal power produced in the carbonator have been assessed.