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Highlights • 1D simulation of the Ca-Cu fixed bed reactors and process integration study. • Economic optimization of the Ca-Cu reactors size and pressure drops through heat exchangers. • Net efficiency 0.5% points higher than benchmark with 89.1% of CO 2 capture efficiency. • ˜5% lower cost of CO 2 avoided cost than the benchmark. Abstract A techno-economic analysis of a natural gas combined cycle integrated with a pre-combustion CO 2 capture process based on the Ca-Cu process has been carried out. An extensive calculation of the balances of the entire power plant has been done, including the results obtained from a 1-D pseudo homogeneous model for the fixed bed reactors that compose the Ca-Cu process. Moreover, a methodology developed by the authors is here presented for calculating the cost of the electricity produced and of the CO 2 avoided. This methodology has been used to perform the economic analysis of the Ca-Cu based power plant and to optimize the size of the Ca-Cu reactors and the pressure drop in critical heat exchangers. An electricity cost of 82.6 €/MWh has been obtained for the Ca-Cu based power plant, which is 2.2 €/MWh below the benchmark power plant based on an Auto Thermal Reformer with an MDEA absorption process for CO 2 capture. The improved performance of the Ca-Cu based power plant in terms of electric efficiency and reduced capital cost expenditure is the reason for the reduced electricity costs. Moreover, a lower cost of CO 2 avoided is also obtained for the Ca-Cu plant with respect to the benchmark (80.75 €/t CO2 vs. 85.38 €/t CO2), which features 89% of CO 2 capture efficiency. [ABSTRACT FROM AUTHOR]

The theoretical approach for the bubble-to-emulsion phase mass exchange in bubbling gas-solid fluidized beds developed by Davidson and Harrison in the early 60’s is still widely applied in phenomenological models, mainly because of lack of more detailed experimental data to improve the description. In this study a novel infrared transmission technique that allows the direct and non-invasive measurement of gas concentration profiles inside bubbles with a high temporal resolution has been used for the validation of the theoretical description for the gas exchange. At first, the experimental technique has been further improved concerning the selective removal of particles raining through the bubbles, as well as the reconstruction of tracer gas concentration profiles throughout the gas bubble. The bubble-to-emulsion phase mass transfer coefficients have been measured by injecting tracer gas bubbles into incipiently fluidized beds and beds at freely-bubbling conditions, for beds consisting of glass beads of different particle size and with different injected bubble diameters. The results show that the Davidson and Harrison approach can reasonably well describe the mass exchange for isolated bubbles injected into a bed at minimum fluidization conditions. However, experiments carried out in a freely bubbling bed have shown that the mass exchange rate is considerably enhanced due to the increased gas through-flow through the bubbles. An empirical correlation (with deviations within only 20%) for the volumetric bubble-to-emulsion phase mass transfer coefficient has been developed based on the bubble size and superficial gas velocity, where it is noted that in this work the convective contribution in the mass exchange is dominant. [ABSTRACT FROM AUTHOR]

Copper oxide on alumina is often used as oxygen carrier for chemical looping combustion owing to its very high reduction rates at lower temperatures and its very good mechanical and chemical stability at temperatures below 1000 °C. In this work, the redox behaviour of CuO/Al 2 O 3 has been studied in great detail together with the redox behaviour of CuO/SiO 2 to identify the main phenomena affecting the observed redox kinetics. Combination of TGA results with detailed characterisation with XRD of the oxygen carriers at different stages during the redox cycling allowed elucidating the causes for the sudden decrease in the reaction rate observed at higher conversions for the CuO/Al 2 O 3 oxygen carriers. The main results of the study can be summarized as: i) oxidation reaction reaches always full conversion independent of the reaction temperature; ii) reduction reaction reaches only full conversion at very high temperatures, showing a significant decrease in the reaction rate at lower temperatures at higher particle conversions; iii) the observed sudden decrease in the reduction rate is related to the spinel reduction of CuAl 2 O 4 and CuAlO 2 . [ABSTRACT FROM AUTHOR]

Thermogravimetric analysis and breakthrough experiments in a packed bed reactor were used to validate a developed adsorption model to describe the cyclic working capacity of CO 2 and H 2 O on a potassium-promoted hydrotalcite, a very promising adsorbent for sorption-enhanced water-gas-shift applications. Four different adsorption sites (two sites for CO 2 , one site for H 2 O and one equilibrium site for both species) were required to describe the mass changes observed in the TGA experiments. The TGA experiments were carried out at operating temperatures between 300 and 500 °C, while the total pressure in the reactor was kept at atmospheric pressure. Cyclic working capacities for different sites and the influence of the operating conditions on the cyclic working capacity were studied using the developed model. A higher operating temperature leads to a significant increase in the cyclic working capacity of the sorbent for CO 2 attributed to the increase in the desorption kinetics for CO 2 . The model was successfully validated with experiments in a packed bed reactor at different operating temperatures. [ABSTRACT FROM AUTHOR]

Copper oxide on alumina is often used as oxygen carrier for chemical looping combustion owing to its very high reduction rates at lower temperatures and its very good mechanical and chemical stability at not too high temperatures. In this work, the redox kinetics of CuO/Al 2 O 3 have been studied at elevated pressures and temperatures. All the experiments have been started under the same initial conditions to assure the same starting point. While other studies reported a negative effect of the total pressure on the redox kinetics, this study shows that this negative effect of the pressure is most probably caused by external mass transfer limitations in previous studies. Additionally, as long as external mass transfer limitations are prevented, the total pressure at which the reduction is performed does not affect the redox kinetics nor the morphological and chemical structure of the oxygen carrier. The sudden decrease in the reduction rate at higher particle conversions was not influenced by the operating pressure and was attributed to limitations in the spinel reduction kinetics. [ABSTRACT FROM AUTHOR]

The use of Carbon Molecular Sieve Membranes (CMSM) for selective CO 2 separation from post-combustion CO 2 -rich streams from steel plant was experimentally evaluated and reported in this paper. Efficient CMSMs were developed for such application and their promising potentials in operating at elevated temperatures and pressures were experimentally demonstrated. The best performance in terms of flux as well as perm-selectivity, above the Robeson upper bound, was obtained using a CMSM developed with ethylenediamine in the dip-coating stage of the fabrication. In fact, adding ethylenediamine was proven to be particularly important in narrowing down the pore size distribution to ultra-micropore and establishing effective CO 2 adsorption site over the membrane surface and the pores wall. It was shown that using a tailored CMSM with a precursor synthesized by co-polymerization of ethylenediamine with Novolac can improve the CO 2 /N2 ideal perm-selectivity from 33 to 97 at operational conditions of 200 °C and 20 bar. • Ethylenediamine helps in narrowing down the pore size distribution of CMSM to ultra-micropores. • CO 2 /N2 ideal perm-selectivity improves from 33 to 97 at operational conditions of 200 °C and 20 bar. • Membranes with high selective CO2-separation, beyond Robeson upper bound, have been developed. [ABSTRACT FROM AUTHOR]

To enable the investigation of the hydrodynamics of gas–solid fluidized bed reactors at high-temperatures and reactive conditions, a new non-invasive experimental technique has been developed, based on the extension of Particle Image Velocimetry (PIV) coupled with Digital Image Analysis (DIA) using dedicated high-temperature endoscopes for image recording and laser illumination. The new endoscopic-laser PIV/DIA technique (ePIV/DIA) allows to determine simultaneously information from the emulsion and bubble phase with high spatial and temporal resolution in a pseudo-2D columns. The ePIV/DIA technique with single-source laser illumination has first been thoroughly validated at cold-flow conditions by comparison with a standard PIV/DIA technique with LED-illumination, showing very good agreement of the results in terms of particle velocity and solids mass flux profiles. The technique has subsequently been applied to fluidized beds in the bubbling fluidization regime at elevated temperatures to demonstrate its unique possibilities to measure detailed bed hydrodynamics at elevated temperatures. [ABSTRACT FROM AUTHOR]

Chemical-looping combustion is an emerging technology for power production with integrated CO 2 capture. With this combination, the energy penalty is expected to be relatively low, provided that the reactors are operated at elevated pressures (20 bar). Packed bed reactors can better accommodate high pressures compared with interconnected fluidized bed systems, while the challenging gas/solid separation is circumvented. In this work, CLC is demonstrated in a lab scale pressurized packed bed reactor using NiO/CaAl 2 O 4 as oxygen carrier material. H 2 and syngas with a typical composition obtained from coal gasification are used as fuel in the reduction step. The pressure has been varied between 2 and 7.5 bar, while it is demonstrated that the pressure has quite a small effect on the overall performance of the CLC reactor. The experiments are well described by a one-dimensional pseudo-homogeneous reactor model, with which it is shown that the required high temperatures for power production can be reached in case the reactor is scaled-up (decreasing the heat losses). A drawback of the oxygen carrier used is that the reduction kinetics depend on the temperature during the previous oxidation, which has been fixed during all the experiments. The reduction kinetics decrease with the oxidation temperature, which is probably caused by interaction with the support material and therefore some further modifications on the support material are required for high temperature applications. In case the process is carried out with syngas and steam, the heat management strategy has to be adapted because of the heat produced by the water gas shift reaction. [ABSTRACT FROM AUTHOR]

The hydrodynamic behaviour of a pseudo-2D Two-Section Two-Zone Fluidized Bed Reactor (TS-TZFBR) with an immersed tube bundle in its lower zone has been studied using non-invasive Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA). Coupled porosity distribution maps from DIA post-processing and solids velocity vector fields from PIV analysis allowed the reconstruction of the transient and time-averaged solid fluxes along the bed. Six different tube bank configurations at several different superficial gas velocities have been tested to evaluate the hydrodynamic behaviour within the lower zone of the TS-TZFBR. The solids axial mixing along the vertical bed position has been quantified for this novel reactor configuration. Besides, the effect of the internals on the gas-solid mass transfer has been estimated by means of bubble size. A five-staggered tube bundle configuration was able to diminish the average bubble size by 30% within the lower bed zone at usual TS-TZFBR gas flow rates, u gas / u mf =3.0, without increasing the solids circulation time dramatically. [ABSTRACT FROM AUTHOR]

This paper deals with the design and operation strategies of dynamically operated packed-bed reactors (PBRs) of a chemical looping combustion (CLC) system included in an integrated gasification combined cycle (IGCC) for electric power generation with low CO 2 emission from coal. The CLC reactors, that employ ilmenite as oxygen carrier, are operated sequentially across the following phases: oxidation, purge, reduction and heat removal. Two different layout configurations have been considered: in the first configuration, all the inlet streams are fed to the PBRs from the same side (“co-current”), while in the second configuration the coal syngas for the reduction and the N 2 -rich stream for the heat removal phases are fed from the opposite side (“counter-current”). The number of reactors required for continuous operation of a large-scale power plant has been assessed to comply with an 8% maximum pressure drop across the reactor for different internal reactor diameters and reactor lengths. A sensitivity analysis on the number of reactors has been carried out by varying the particle size, while accounting for the effect of internal mass transfer limitations. A novel strategy for the dynamic operation of the reactors is proposed to reduce gas temperature fluctuations at the inlet of turbomachines and heat exchangers by switching the reactors in parallel with a proper phased displacement. A comprehensive analysis has been carried out on the dynamic reactor behaviour by using a one-dimensional adiabatic reactor model. The outcomes from the reactor model have been used to calculate the resulting conditions of the gases that are leaving the reactors operated in parallel. The results obtained indicated that 14–16 units (for the co-current and counter-current configuration respectively) with 5.5 m of internal diameter and 11 m of length are required for continuous operation of a 350–400 MW e coal-fired power plant. Although packed-bed reactors are dynamically operated, the gases released by the CLC units do not exhibit significant transient temperature changes (only about 6 °C for the gas turbine) and the system seems promising for future large-scale power plant applications with integrated CO 2 capture. [ABSTRACT FROM AUTHOR]

• Biomass from contaminated soils to renewable energy production. • Study for the choice of the most performing material for a fluidized bed gasifier. • The metals release from bed materials was never properly assessed up to now. • Study of TGA – ICP/MS method to predict the syngas contamination from heavy metals. The interaction between biomass from plant assisted bioremediation processes PABR contaminated with heavy metals and the bed materials used in Fluidized Bed Gasifier FBG systems was experimentally studied to identify the origin of the metals detected in syngas and/or solid residues, and affecting the quality of the produced fuels and biochar. The characteristics of an arboreal (poplar pruning) and an herbaceous biomass (Arundo Donax), both previously used in phytoremediation processes, were evaluated. The bed materials have been identified among those most used in pyrogasification processes, such as olivine, K-feldspar, kaolinite and calcite. The simulation of the process and the sampling of the syngas was carried out by means of an instrumental apparatus composed of TGA-DSC connected with a system of bubblers for the capture of heavy metals HM. The analysis of the matrices and the bubbled solutions in ICP-MS allowed to experimentally evaluate quantity and composition of HM released. The analyses showed that calcite gives the best results for both arboreal and herbaceous biomass but it has the disadvantage of losing about 55 % in weight during the process, releasing CO and CO 2 and becoming CaO. The criteria for choosing the most suitable material for the bed of an arboreal or herbaceous biomass gasification were carried out mainly on the basis of the heavy metals released during the process. The study provides useful results for the assessment of the bed materials in FBG conversion process using PABR biomass. From a comparison between all the parameters considered and the Principal Component Analysis (PCA) results, it emerges that K-feldspar represent the best optimization for the materials that can be used in FBG beds both in the case of arboreal and herbaceous plants, while olivine is particularly effective only with arboreal biomass. [ABSTRACT FROM AUTHOR]

A novel experimental technique using a high speed Infrared (IR) camera combined with an improved Digital Image Analysis (DIA) method for non-invasive concentration measurement with high spatial and temporal resolution has recently been developed by Dang et al. (2013). This paper reports the extension of the IR technique to freely bubbling and turbulent fluidization regimes to investigate and quantify lateral gas mixing characteristics in gas-solid fluidized beds. The mechanism of lateral gas mixing in the bubbling regime studied with the novel technique is in good agreement with values reported in the literature. The experimental results, interpreted with a plug flow model with superimposed dispersion for a homogeneous flow, show that the lateral gas mixing coefficient first increases with the increase of superficial gas velocities from the bubbling to the turbulent flow regime and then decreases for even higher velocities, which is consistent with earlier literature studies. The dependency of the lateral gas mixing coefficient on the Reynolds number using Amos׳ correlation (Amos and Mineo, 1993) has shown large discrepancies at low gas velocities (where the equation was extrapolated), while a good match was obtained at higher gas velocities. The experimental findings reported in this paper indicate that the novel IR/DIA technique can successfully be applied for mass transfer and gas mixing studies in gas-solids multiphase flows. [ABSTRACT FROM AUTHOR]

Chemical-looping combustion can be carried either in circulating fluidized bed reactors or in dynamically operated packed bed reactors. In this work, the influence of the reactor selection on the overall process efficiency has been estimated. The CLC reactors are fed with syngas at 20 bar, which is produced from coal gasification. In the fluidized bed system, the oxygen carrier particles are transferred from the air to the fuel reactor and vice versa. Uniform reactor temperatures can be maintained due to internal solids circulation and vigorous mixing. Due to the large solids circulation and low reaction enthalpy in the syngas-fed fuel reactor, small temperature differences result between the reactors. A case where NiO/Al2O3 is used as oxygen carrier has been considered and an LHV efficiency of 41.4% has been calculated, assuming the fuel conversion at chemical equilibrium, leading to some unconverted CO and H2 in the reaction products. If full gas conversion is obtained by using another oxygen carrier operating at the same maximum temperature of 1200 °C, this efficiency can be increased to 41.8%. In the packed bed case, large temperature gradients inside the reactors are obtained and the CO2 and steam is produced at a lower (time-)average temperature. In addition, thanks to the lower average reaction temperature during fuel oxidation, the selectivity of the reduction reactions with nickel is not an issue. On the other hand, in this case a significant amount of steam has to be added or recycled to avoid carbon deposition, leading to an LHV efficiency of 41.1%. If a carrier is selected with a low kinetic activity for the Boudouard reaction, the efficiency can be increased by 1.1% point up to 42.2% of LHV. Other differences between the two systems are related to the number of vessels needed and the volume of the solids inventory, which is expected to be lower in the circulating fluidized bed system. An initial investment cost estimation demonstrates that the oxygen carrier costs are important, so that a low cycle time and a cheap oxygen carrier is preferred. The process efficiency for both reactor configurations is at the same level, 41-42% of LHV. Therefore, it can be concluded that the reactor selection will not be made based on the process efficiency, but on the availability, operability and cost of high temperature and high pressure reactor systems, that are still under development and both present pros and cons. [ABSTRACT FROM AUTHOR]

A detailed thermodynamic analysis has been carried out of large-scale coal gasification-based power plant cycles with near zero CO2 emissions, integrated with chemical looping combustion (CLC). Syngas from coal gasification is oxidized in dynamically operated packed bed reactors (PBRs), generating a CO2-rich stream ready for sequestration. PBRs have recently been proposed for CLC as an alternative for an interconnected fluidized bed reactors system operated at high pressure, to circumvent difficulties associated with solids circulation and gas/solid separation at high temperature and pressure. However, in view of the dynamic operation, the heat management in PBRs needs to be carefully assessed, since it affects the temperature and gas flow rates at the reactor outlet during the different cycles. The present work investigates the effect on plant performance of two different PBRs heat management strategies proposed in a previous work, with the aim of avoiding problems related to oxygen carriers featuring low reduction kinetics at moderate temperatures. The system is designed to achieve full integration of the steam cycle with the other units of the plants in order to improve the overall plant efficiency. A sensitivity analysis on the CLC operating pressure, the steam cycle parameters and the effect of syngas dilution with exhaust recirculation and steam addition was performed. The mass and energy balances of the integrated plant are presented in detail and the plant performance is compared with reference technologies. The net electric efficiency approaches 41% (based on the coal LHV) with a CO2 capture efficiency over 97%. Moreover, it has been found that the heat management strategies adopted do not significantly affect the maximum net electric efficiency, even if different power shares between the gas and steam turbines are obtained, with consequent implications in the plant design and economics. [ABSTRACT FROM AUTHOR]