Study of Properties of a Catalyst for Soot Post-Combustion by Thermogravimetry-Mass Spectroscopy (TG-MS) Analysis

The intent of this work is to study the performance of a catalyst for soot combustion under reducing and oxidizing environments, to draw indications on the catalytic mechanism and on the implications of the sulfation process. Thermogravimetric (TG) analyses of the sulfated catalyst in reducing and oxidizing environments and on-line mass spectrometry (MS) analyses of the gaseous products of the TG analyses have been performed. The catalyst is able to reduce and oxidize, when treated in suitable environments. Both H2 and carbon reduce the catalyst within comparable ranges of temperature, although the main products of the reductions are different. In addition, the temperature ranges within which the catalysts reoxidize after the reductions are practically coincident with the catalyst threshold temperature. The aforementioned findings have led us to address the catalyst reduction as the rate-limiting step of the soot oxidation process. Sulfation decreases the catalyst activity through two different mechanisms that involve different catalytic components. One, which is irreversible, is due to the chlorine substitution with sulfur, and the other, which is reversible, is likely related to the physical or chemical covering of some other catalytic compounds that do not contain chlorine initially

The role of the terrain geometry on the flames propagation through a vegetative fuel bed

When a wildland fire occurs the domain geometry is a key parameter in governing the way the fire spreads across the terrain. The effect of this variable on the rate of flames propagation was investigated in this work by means of a computational fluid dynamics software specifically designed to simulate fires in wildland environment. The physics-based model - i.e. relied on the laws of conservation of momentum, energy and mass – was adopted under two different domain configurations (double-slope domains and canyon); the capability of the computational code to correctly predict the fire behaviour was verified by comparison with results of experimental tests available in the literature

Modelling of a Catalytic Micro-Reactor Coupling Endothermic Methane Reforming and Combustion

In this study the mathematical modelling of a catalytic microstructured plate reactor for the production of hydrogen was performed in 2D and 3D geometry. The proposed reacting system uses the heat generated by an exothermic reaction (combustion) to sustain endothermic reforming reactions. Therefore, it pertains to those devices useful for producing the feed for fuel cell system for the remote generation of electrical power. However, because of the compactness of the reacting system it can also be considered in the context of apparatus aiming at process intensification. Within this frame the catalytic contribution of both exothermic and endothermic reactions was modeled considering the classic Langmuir- Hinshelwood surface kinetic theory. The advantage of using a real 3D geometry configuration consists in the possibility of considering the importance of the entering and boundary effects with particular attention to fluid stagnation and heat hot spots. The trade off of such a choice is certainly the huge increase of computing time and/or of the power of the computing facility. With respect to other works performed with similar reactor geometry and reacting systems this does not use simplifying assumptions such as catalyst layers modeled by one-dimensional approach, fully developed laminar flow or transverse heat and mass transfer taken into account through lumped heat and mass transfer coefficients. Results of simulations presented here concentrates on the comparisons between results of: countercurrent (CTC) and concurrent (CNC) flow patterns of the reactant streams; of simulations carried out with 2D and 3D models and of the influence of the thickness of the catalytic layers on the reactor performance. Simulations indicates that CNC flow pattern of reactants streams allows a better performance of the reactor since positive temperature differences between the catalyst layers and the gas in the channels maintain along the whole reactor and, consequently, there are not heat flux inversions, which occur under CTC flow pattern. Results also showed that as concerns an adiabatic reactor, whatever the operating conditions, 2D and 3D models yield substantially the same results. Finally, modelling demonstrated that for a realistic catalyst layer configuration thicknesses larger than 50 _m are useless for enhancing the reactor performance. The feasibility of the model proposed may show its potential in fast and easy implementation of several combustion and reforming fuels so to significantly enhance the performance prediction of real processes

Micro-Scale Catalytic Reactor for Syngas Production

This paper presents both experimental and modeling investigations of a catalytic wall fuel processor consisting of coupled methane reforming and methane combustion sections. The reacting systems are both catalytic and the latter generates the heat required for the occurrence of the former. The catalytic wall reactor was examined for light-off behavior and for steady-state product distribution. On one hand, the analysis of the reaction products distribution after catalyst ignition indicated that in both combustion and reforming sections catalysts undergo to a relatively long transient (about 40 min) before reaching steady state conditions. On the other hand, a much longer reactor thermal transient was observed and the two transient behaviors appear independent of each other. Analysis of the reactor operating under real conditions (nonadiabatic) showed that a 3D model is needed to accurately predict the reactor performance because a 2D model, although much more convenient, cannot allow for the whole heat loss thereby yielding unreliable results

Biopolitica di Alfredo Cospito

In this article, the author analyses the case of anarchist Alfredo Cospito, in hunger strike for protesting against his carceral condition

Fire behaviour in canyons due to symmetric and asymmetric ignitions

The eruptive propagation of a fire is a particular behaviour characterized by a sudden increase in the rate of spread and intensity without any change in the external driving forces such as wind velocity and ambient temperature, vegetation type and moisture content. It is, therefore, a local or internal dynamic connected with the terrain configuration and the ignition position that regulates fire spreading and causes its acceleration. This phenomenon is particularly evident and common in canyons. This work aims to study the effect ignition position on the fire propagation in a canyon by means of a physically-based computational code. The code WFDS was shown to be effective to describe the fire behaviour throughout such a terrain configuration