This paper aims to provide a review of past and recent research activities performed to combine endothermic and exothermic reactions. Attention has been focused on the recuperative and direct coupling employed to process fuels in order to obtain hydrogen, especially for a distributed use as feed for small scale fuel cells systems. Moreover, information about reactors performance obtained in the two configurations is reported along with the methods used to remove CO and separate hydrogen or other high-value products through the use of membranes. In this context, techniques employed by researchers to study these reactors along with the role that modelling has in the development process are also described.

A numerical code, based on a physical model, is used to perform simulations of a fire developing over a relatively large real terrain. The paper shows how a physics based model can be efficiently used to study the behaviour of a fire propagating over a large area with a real surface configuration. In particular, the code provides information about fire front shape profiles and terrain area burned in time. The proposed method of employment of the simulation software is compared with data, available in the literature, concerning a piloted fire accident occurred in central Portugal in 2001. The comparison between the experimental and the modelled results shows a good agreement and may suggest that this model may serve as the basis for an on going prediction method.

This work investigated a micro-scale catalytic plate reactor designed for thermal coupling of an exothermic reaction (combustion) to endothermic reforming reactions. The system was studied through both experiments and modelling. A 3D model, previously developed by the authors, was employed and adapted to simulate the real reactor geometry. The aim of the work was to study the influence of different kinetic sub-models for the reforming reactions on the model results. Multi-component mass transport was modelled using a Fick-like law. Operating conditions utilized in the experiments and for the modelling were those typical of reforming reactions. The kinetics sub-models of the methane reforming and combustion reactions were taken from the literature. In particular, for the combustion process a power-law kinetic expression was used with a linear dependence on methane concentration and zero dependence on oxygen concentration. Instead, for the reforming reactions two different kinetics, suggested, respectively, by Xu and Froment and by Hou and Hughes, were employed. The comparison between model results and experimental findings was performed to discriminate which of the two reforming kinetics was more suitable to describe the experiments. It was found that when using the reforming proposed by kinetics Hou and Hughes was employed, the agreement between model results and experiments was elevated while it resulted poor when the other kinetic sub-model was used. An analysis of the features and of the origins of the two sub-models was performed and the comparisons with the characteristics of our experiments was carried out in order to find the reasons for the different agreement.

In this work the way the wind and terrain inclination affect the fire propagation across a homogeneous fuel bed was investigated. The role played by these two parameters in fire behaviour was studied, showing that wind velocity affects the rate of spread more strongly than the terrain slope. The evolution of a fire front from a linear ignition source was analysed along with the time evolution of the fire front according to the external condition. The role played by the terrain slope and atmospheric wind in determining the rate of spread was quantified, showing how the latter parameter has a stronger dependency on the rate of fire spreading.

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 modelled 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 µm 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.

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.

Over the last decades, wildfires phenomenon has assumed alarming proportions. Woodlands in rural areas or at the interface with urban areas still continue to burn with significant environmental, social and economic impacts, in particular in case of increased frequencies of fires. As a response, a number of technologies have been developed for the management of environmental emergencies. Since fire behavior and propagation is one of the most critical aspect of the decisional structure during emergencies, for a decision support system the development and the validation of a model for short term prevision of fires propagation is of primary importance. In wildland fires, flaming combustion of lignocellulosic fuels occurs when the gases released from the thermal degradation ignite in the surrounding air. Then the heat of combustion causes the thermal degradation of adjacent virgin fuel. A successful fire spread (speed of the fire) occurs when sufficient energy is transferred from the flame front to the unburnt solid fuel, resulting in an increase in the fuel temperature to its ignition point. The solid phase temperature is the result of interacting radiative, conductive, and convective heat transfer. In addition, water vaporization, pyrolysis, and fuel combustion also influence the solid phase temperature. Fire spread is not only the propagation of fire following the terrain slope, but also the propagation of fire from surface fuels (litter, grass, shrubs) to crown fuels (foliage of tree crowns). Knowledge of these effects and their quantification is crucial for the phenomenon prediction. Since the difficulty in performing real scale tests, a range of wildfire behaviour models exist, which vary in both complexity and computational cost: empirical models (based primary on statistics collected by observation of experimental or historical fires) [1], semi empirical models (based on physical laws, but enhanced with some empirical factors) that are widely used as operational tools [1], and physical models which attempt to solve the equations governing fluid dynamics, combustion, and heat transfer, accounting for the fire/atmosphere and the fire/fuel interactions [2]. The problem involves strong interaction between non-linear phenomena such as the turbulence in the lower part of the atmospheric boundary layer, chemical reactions, radiation heat transfer in the flaming zone, and the degradation of heterogeneous media representing the vegetation and its interaction with the ambient gas mixture (air, pyrolysis and combustion products). In this context the present work aimed at studying fires propagation by means of a CFD code properly modified to be able to simulate fire spreading among different kind of fuels (trees, shrubs and ground litter). Mathematical tools applied to this kind of environment can be used to understand how fires spread in a forest, to help train fire fighters and to quantify the benefits of mitigation actions. Due to the complex phenomena involved in simulation, detailed data on the topography, local meteorology, elevations, three-dimensional distributions of natural fuels, and their properties are needed [3].

This paper reports a modelling study for steam reforming of methane occurring in a microstructured catalytic reactor. The geometry adopted for modelling was tailored on a real lab-scale system and reflects a configuration commonly adopted in literature [1-2-3], where heat generated by methane combustion substains endotermic reactions (CH4 reforming). Mathematical simulations of this kind of system are important research tools for the investigation of the complex phenomena governing system performance and for suppling information about parameters that cannot be detected by real measuring devices. In developing microchannel reactors for the methane steam reforming, understanding the temperature profile within the reactor is important for designing and optimizing the structure of catalysts to achieve the maximum performance. Numerous studies investigated the modelling of methane reforming and its related kinetics in micro-reactor especially on Ni catalysts [4-5-6]. Nevertheless, the topic was not widely investigated under a non-adiabatic restraint [7-8-9], where the need to adopt a 3D geometry becomes unavoidable. Furthermore, few comprehensive studies extended the energy and mass balance of the reactive flow within the thin catalytic layers (50 μ) [10-11]. On the contrary, simplified models are available in the literature where temperaure and concentration profiles are assumed constant along the catalyst thickness limiting, therefore, the possibility to use modelling as a design tool for the catalyst configuration. In this work, the modeling study was performed in a 3D geometry, solving the fully coupled problem of chemical reactions taking place inside catalytic layers with laminar flow occuring in an adiacent channel including mass diffusion due to thermal and concentration gradients. The contribution of the catalytic reforming reactions was modelled considering two different kinetic expressions suggested in the literature by Xu and Froment [4] and by Hou and Hughes [5]. Results of the simulations were compared with pertinent experimental results showing that a good agreement is achieved when applying the kinetic expressions suggested by Hou and Hughes.

This work reports on the experimental investigation of the performance of a microstructured catalytic reactor where simultaneous methane catalytic combustion and steam reforming occur. The reactions take place over catalytic layers deposited on the opposite faces of the same metallic slab so that combustion heat sustains the endothermic steam reforming reaction occurring on the opposite side of the slab that also separated the channels where the reactants are fed. The system may operate both in co-current (CNC) and counter-current (CTC) flow. Under the tested conditions the best reactor performance was about 60% of methane conversion to syngas with a hydrogen yield of 3.33 when gas mean residence time in the reforming channel (τsr) was about 55 ms and the molar steam/methane feed ratio 3. An oxygen-lean stream (molar CH4/O2=1/1.68 - O2 in air) was fed to the combustion channel because higher oxygen concentration negatively affected the catalytic combustion kinetics. Even if a relatively high thermal dissipation strongly limited the thermal efficiency of the process, autothermal stability of the system was proved to occur both in CTC and CNC flow patterns when the mean residence time in the combustion channel (τco) was around 33 and 66 ms and the CH4/O2 ratio 1/1.68, while in the reforming channel τsr was about 55 ms. 1. Experimental setup The experimental setup includes reactants feed, reactor and product analysis. The reactants for the exothermic and the endothermic reactions can be fed in CNC or CTC mode. Cylinder air and methane were delivered and metered by mass-flow controllers, (Brooks SL5800) while the feed water flow was regulated by a peristaltic pump (Gilson). The reactants entered the reactor at about 500°C while the reactor was pre- heated at 600°C. Electrical heaters and related temperature controllers were employed for pre-heating the reactor and the entering gas streams. The reactor exhaust products concentrations were monitored by ADVANCE OPTIMA, ABB analyzers: specifically, CH4, CO and CO2 by a NDIR analyzer (Uras 14), O2 by a paramagnetic analyzer (Magnos 106) and H2 by a thermoconductivity analyzer (Caldos 17).

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.