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Herce C.,Research Center on Energy Resources and Consumptions | Stendardo S.,New Energy Technologies | Cortes C.,University of Zaragoza
Chemical Engineering Journal | Year: 2015

The high-temperature, solid chemical looping for CO2 capture is a promising technology to mitigate greenhouse gases emission. The choice of a high-performance sorbent is a fundamental need to improve the CO2 uptake in solid regeneration systems. Calcium-based sorbents have demonstrated a good compromise between cost, performance and environmental impact. In particular, calcined dolomite is selected as CO2-acceptor in pre-combustion processes due to its good experimental capacity for CO2 uptake. Moreover, among the solid acceptors investigated in scientific literature, naturally occurring sorbents (e.g. calcite and dolomite) are not considered as potentially hazardous substances, as they are not toxic either to the environment or to humans. This work presents the effect on CO2 carrying capacity of different compositions of the calcination atmosphere, from 100% N2 to 50/50% CO2-N2, as well as a novel pre-treatment (here called triggered calcination) by means of half-calcination in CO2 with subsequent flash N2 calcination. This new decomposition method improves CO2 capture up to 24% in prolonged carbonation/calcination cycling (over 150 cycles). Other factors have been studied such as heating rate, CO2 concentration and carbonation time, as well as other pre-treatments. Increased and sustained rates of CO2 uptake can be explained as a result of changes in the internal structure of sorbent particles. In order to explain them, a study of the surface area has been carried out by means of an indirect method based on TGA experiments. © 2014 Elsevier B.V.


Herce C.,Research Center on Energy Resources and Consumptions | Herce C.,ENEA | De Caprariis B.,University of Rome La Sapienza | Stendardo S.,ENEA | And 2 more authors.
Journal of Thermal Analysis and Calorimetry | Year: 2014

Coal gasification and combustion are strongly dependent on devolatilization step. Aim of this work is to obtain the parameters of global kinetics of devolatilization of a sub-bituminous coal with high sulfur content. The kinetic parameters are obtained by means of TG experimental data, and applying different approaches to extrapolate the data to industrial relevant conditions. The simpler method is a model-free one which supposes a single step process whose Arrhenius kinetic parameters (A and E a) have to be determined. Another common approach is the distributed activation energy model (DAEM) which assumes a series of first order parallel reactions occurring and sharing the same pre-exponential factor, A, with a continuous distribution of the activation energy. For the fitting of the experimental data, a numerical solution to DAEM and two approximate methods have been evaluated. Moreover, the results of these kinetic methods based on empirical approaches were compared with simulated data obtained using a more complex model based on percolation theory with cross-linking mechanism and vapor-liquid equilibrium (chemical percolation devolatilization, CPD model), which allows to simulate the coal pyrolysis from volatile yield data. © 2014 Akadémiai Kiadó, Budapest, Hungary.


Guedea I.,Research Center on Energy Resources and Consumptions | Diez L.I.,Research Center on Energy Resources and Consumptions | Pallares J.,Research Center on Energy Resources and Consumptions | Romeo L.M.,Research Center on Energy Resources and Consumptions
Chemical Engineering Journal | Year: 2011

This paper addresses the mathematical development and the experimental validation of a semi-empirical model designed to characterize the fluid-dynamic response of a fluidized bed reactor under oxy-fuel operation. The objective is to survey the main differences between a conventional air operation and a novel O 2/CO 2 operation, as for the interactions of solid-phase and gas-phase. The model provides all the relevant variables describing the fluid-dynamics, and it is conceived to simulate the performance of a lab-scale facility. Data gathered from the cold- and hot-operation of a 90 kW th oxy-fired fluidized bed are used for validation purposes. Bed porosity, minimum fluidization velocity and bubbles' size are detected to change under oxy-firing conditions. Once validated, the tool will be used to predict the performance under new fluidizing atmospheres and will be integrated within an entire model coupling fluid-dynamics, combustion and heat transfer phenomena. © 2011 Elsevier B.V.


De Caprariis B.,University of Rome La Sapienza | Santarelli M.L.,University of Rome La Sapienza | Scarsella M.,University of Rome La Sapienza | Herce C.,Research Center on Energy Resources and Consumptions | And 2 more authors.
Journal of Thermal Analysis and Calorimetry | Year: 2015

Pyrolysis is a fundamental step in thermochemical processes of biomass materials, so a suitable kinetic model is an essential tool to predict the evolution of the resulting products of reaction. However, many difficulties arise in modeling this process step due to the very high number of the involved reactions. In this work, a new double-Gaussian distributed activation energy model was applied in fitting the experimental data of olive residue pyrolysis obtained by thermogravimetric analysis. 2-DAEM formulation considers two sets of parallel reactions occurring and sharing the same pre-exponential factor, but shows different distributions of the activation energy, described by two separate Gaussian distributions that, in turn, grasp the two pyrolysis steps with a high accuracy. Since it is well known that in fitting all the kinetic parameters the pre-exponential factor results highly correlated with the activation energy, the former parameter was separately estimated as a linear combination of the values obtained for the three main biomass components, cellulose, hemicellulose and lignin. © 2015 Akadémiai Kiadó, Budapest, Hungary.


De Caprariis B.,University of Rome La Sapienza | De Filippis P.,University of Rome La Sapienza | Herce C.,Research Center on Energy Resources and Consumptions | Verdone N.,University of Rome La Sapienza
Energy and Fuels | Year: 2012

Understanding and modeling of coal pyrolysis assume particular importance, since it is the first step of combustion and gasification processes. The complex reactions occurring during pyrolysis lead to difficulties in the process modeling. The aim of this work is to find a global kinetic model that well represents the pyrolysis of two different coals with opposite rank, a sub-bituminous and an anthracite coal, in order to carry out the kinetic parameters of the process. The Distributed Activation Energy Model (DAEM) was used to fit experimental data obtained with a thermogravimetric analysis. The model assumes that a series of first order parallel reactions occurs sharing the same pre-exponential factor, k 0, and having a continuous distribution of the activation energy. One of the limits of the standard Gaussian DAEM is that with this model is not possible to distinguish the primary from the secondary pyrolysis. A two Gaussians DAEM was developed considering that two classes of reactions take place having the same k 0 and different distribution of activation energy. Since in the model k 0 is highly correlated with the mean activation energies, it was fixed at characteristic values taken from literature. © 2012 American Chemical Society.

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