Ángela Millera

Kinetics of pyrolysis of high density polyethylene. Comparison of isothermal and dynamic experiments

Abstract An experimental study of the thermal decomposition of high density polyethylene in an inert atmosphere has been carried out. Both isothermal and dynamic experiments at different heating rates have been performed in a thermobalance. The objective of this work is to analyse the applicability of a simple first-order equation to the prediction of the weight loss of the material, taking into account the complex chain reaction mechanism. The corresponding kinetic parameters have been obtained and its applicability at different heating rates has been analysed. The isoconversion method of Ozawa–Flynn–Wall has been used to obtain the activation energy and the frequency factor from non-isothermal experiments and compare them with the values obtained from isothermal experiments and with the results obtained by other authors.

Kinetics of thermal decomposition of cellulose: Part I. Influence of experimental conditions

The kinetics of weight loss in the thermal decomposition of cellulose have been determined by means of isothermal and dynamic experiments carried out under various conditions. Values for the pyrolyzable fraction, reaction order and kinetic constant have been obtained from isothermal experiments, while the important influence of the rate of heating of the system as well as the percentages of pyrolyzed solids at T ⩽ 150°C have been observed from the dynamic experiments.

Evaluation of the use of different hydrocarbon fuels for gas reburning

Abstract Gas reburning is a NOx reduction technique that has been demonstrated to be efficient in different combustion systems. An experimental study of gas reburning performance in the low temperature range (at and under 1100°C) has been carried out. An evaluation of the use of different hydrocarbon fuels, such as natural gas, methane, ethane, ethylene and acetylene was performed and the influence of the temperature and stoichiometry is considered. The results show that the reburning process is effective under appropriate conditions at the low temperatures used in this work. However, as the temperature diminishes, the influence of the reburn fuel becomes more marked and the use of acetylene or ethane and ethylene leads to better performance than natural gas or methane, the classical reburn fuels for high temperature applications.

Thermal decomposition of lignocellulosic materials: influence of the chemical composition

Abstract The results obtained with different lignocellulosic materials (“Pinaster” pine and barley straw) are compared with those calculated by considering the weighted contributions of the different constituents of the materials. The results obtained in isothermal and dynamic experiments with “Pinaster” pine showed a good agreement, whereas higher divergences were found for barley straw. A different method of data analysis is proposed for barley straw, which uses results directly obtained with this material.

Kinetics of weight loss by thermal decomposition of xylan and lignin. Influence of experimental conditions

The kinetics of weight loss in the thermal decomposition of xylan and lignin in a nitrogen environment have been studied thermogravimetrically. The data from this study are analysed in the light of previous conclusions obtained with cellulose. The results from isothermal and dynamic experiments at different heating rates are related by using the results of dynamic experiments with low heating rates (1.5 °C min−1) as a reference.

Kinetics of weight loss by thermal decomposition of different lignocellulosic materials. Relation between the results obtained from isothermal and dynamic experiments

Abstract The kinetics of weight loss in the thermal decomposition of Pinaster pine and barley straw in a nitrogen environment have been studied. The results obtained under different experimental conditions are shown and compared. These results are related by using the results of dynamic experiments with low heating rates as a reference.

Theoretical study of the influence of mixing in the SNCR process. Comparison with pilot scale data

Abstract A theoretical study of the influence of mixing on the selective non-catalytic reduction (SNCR) process has been performed. The study includes the use of a detailed kinetic reaction mechanism together with a simple approach for mixing based on the “maximum mixedness model” proposed by Zwietering (1959) . Two different configurations for that simple mixing approach have been considered and discussed, i.e. the “direct approach” which implies entrainment of the jet flow (containing the SNCR reduction agent) into a bulk flow (containing the products of the main combustion zone); and the “reverse approach” which represents entrainment of the bulk flow into the jet stream. The main features of both approaches applied to the SNCR process are analyzed and discussed. Furthermore, comparison of the results obtained with the present approaches with different experimental pilot scale results is performed.

Kinetics of thermal decomposition of cellulose: Part II. Temperature differences between gas and solid at high heating rates

Abstract The use of high heating rates when studying the thermal decomposition kinetics of cellulose gives rise to a gap between the solid temperature and the thermogravimetric system temperature. A model is proposed which accounts for this temperature gap and permits the calculation of the actual solid temperature. The results for various heating rates are fitted using the same kinetic equation.

Characterization of Soot

The characterization of physical and chemical properties of the carbon particulate matter commonly named soot is relevant in the research on pollutants emitted in the atmosphere from combustion and industrial plants. The selection and the standardization of advanced analytical methods are necessary to provide reliable and reproducible results on the characteristics of carbon material. This chapter reports an overview of the main off-line techniques available to characterize carbon materials as: elemental analysis, physical adsorption with the determination of the specific surface area, electronic microscopy techniques, X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, infrared spectroscopy, soot reactivity toward O2 and NO, UV–Visible spectroscopy, size exclusion chromatography and fluorescence spectroscopy. The results of the implementation of these techniques on a commercial standard carbon material (Printex-U carbon black), considered as analog of soot, are reported as case study.

Experimental and Kinetic Study of the Interaction of a Commercial Soot with NO at High Temperature

An experimental and kinetic study at high temperature was made of the interaction of NO with Printex-U, a commercial carbon black, considered as diesel soot model compound. Foremost, a characterization of this soot was performed by using different techniques such as elemental analysis, BET surface area analysis, SEM, TEM, and XRD. Two series of experiments were carried out. The first one took into account the inlet NO concentration influence (from 200 to 2000 ppm) at a given temperature of 1273 K. In the second one, the temperature influence (from 1173 to 1373 K) at a given NO concentration of 2000 ppm was considered. From the experimental results, a strong effect of the inlet NO concentration and temperature was observed. A kinetic model, the shrinking core model with decreasing size particle and chemical reaction control, was successfully applied, obtaining a fractional reaction order of 0.26 with respect to NO and activation energy of 110 kJ/mol.