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The strategy to stabilize distributed combustion regimes adopting cyclonic flow fields has been proven to be challenging. In fact, the establishment of a toroidal flow field within a combustion chamber may ensure the recirculation of mass and sensible enthalpy required to simultaneously dilute the fresh reactants and increase the temperature above the autoignition one. The combination of reactants dilution and preheating may greatly increase system energy efficiency and lower pollutants production producing very peculiar combustion regime (named MILD Combustion). At the same time this strategy can be compromised if the sensible enthalpy is not high enough to promote the auto-ignition process of diluted mixtures. This may happen either because of an inefficient recirculation system or due to a too low calorific fuel. The paper aims at exploiting the performance of a small-size cyclonic burner for a conventional fuel (CH4) and a low calorific fuel (synthetic biogas) through the characterization of the process stabilization and pollutant emissions as a function of the mixture equivalence ratio and the nominal thermal power of the inlet mixture (from 2 to 10 kW), with the aim of identifying the optimal operating condition of the system. Results suggest that the system has to be exercised with mixtures with compositions slightly under the stoichiometric conditions and in a well identified temperature range to minimize both NOx and CO emission. The burner can be easily exercised also with low calorific fuels for higher thermal powers according to the low LHV. However, it results that an efficient recirculation of the exhausts produces a robust MILD combustion condition also when low calorific fuels are used.

This study analyses the effect of inorganics in biomass pyrolysis and gasification. The experiments were carried out at low heating rates to isolate the chemical reactions from heat and mass transfer limitations. Three different types of biomass were used: walnut shells, hardwood and softwood. The experimental results clearly show the catalytic effects caused by the presence of inorganics and that these effects are enhanced in the samples with higher potassium concentration. In addition, a kinetic model was implemented in Python using Cantera chemical kinetics library and a kinetic mechanism that includes product speciation was considered. Model predictions show that an optimized mechanism follows the demineralized experimental profiles with slightly better accuracy, when compared with the raw experimental profiles. Nevertheless, the optimized mechanism is not able to predict the gas phase release. Experimental tests that include the collection of liquids are necessary to provide additional data for supporting the improvement of the current pyrolysis kinetic mechanism. In this respect, before including the effects of gasification and alkali and alkali earth metals in the mechanism, it is crucial to firstly predict with accuracy the pyrolysis experimental profiles., Proceedings of the 30th European Biomass Conference and Exhibition, 9-12 May 2022, Online, pp. 794-800

Even in the presence of the formidable growth of renewable energy sources, advanced combustion processes have and will continue to have an irreplaceable role as a driving force for energy market. This is indeed motivated by the same huge amount of energy that can be conveniently stored in the form of energy carriers, made available from the renewable sources. The coupling of the appropriate combustion conversion technology with locally available biofuels certainly is among the most effective solutions, now on the table, to face the decarbonization challenge. In this framework, moderate or intense low oxygen dilution (MILD) combustion is among the best candidates to support the transition toward the net zero emission target. Indeed, due to its inherent features, it is highly fuel flexible and efficient, allowing for the utilization of whatever energy carrier can be considered in the decarbonization strategy. It is also characterized by an inherent low or absent pollutant emission. The novelty of this minireview is to highlight the relevance of the kinetics involved in MILD combustion processes with particular focus on biofuels, identifying invariant temperatures, relevant for process stabilization for any energy carrier. A critical evaluation of advantages and drawbacks of the use of raw bioliquids in MILD combustion conditions is reported. Then, challenges, open questions, and future perspectives on the use of biofuel in MILD combustion are discussed.

This work provides an insight into the influence of the design parameters, specifically the configuration of the outlet section, on the fluid dynamic field and residence times distribution of a cyclonic flow burner, designed to operate under Moderate or Intense Low oxygen Dilution (MILD) combustion conditions with alternative energy carriers. The investigated geometric parameters play a key role in determining the velocity pattern and mixing process of the reactant mixture, fluids residence time distribution and burned gas internal recirculation, by influencing the oxidation process efficiency and pollutant emissions. These latter characteristics are essential in the framework of the recent global energy transition toward renewable sources. Indeed, the intermittency of renewables sources requires the development of specific processes and technologies able to mitigate their inherent variability. Among them, chemical storage ensures large storage capacity for long period and with high efficiency, ensuring easy and safe transportation and storage. In this context, bio-derived alcohols and free carbon fuels such as ammonia and hydrogen have been identified as alternative energy carriers to efficiently storage the renewable energy. Nevertheless, the exploitation of these molecules poses some relevant challenges. The most considerable obstacles are related to the variable composition of the bio-derived products and the consequent lower heating value with respect to traditional hydrocarbon fuels. These aspects greatly limit the technologies capable of employing such energy carriers. Therefore, it is necessary to identify innovative thermochemical conversion technologies highly flexible with respect to the type and composition of the fuel, which ensure reduced pollutant emissions and the stability of the oxidation process for each required operational condition. In this respect, MILD combustion represents an efficient technology matching these issues. In this context, the obtained results allow to identify the appropriate design features of a cyclonic flow burner in order to ensure the complete conversion of the inlet charge and the effective process stabilization.

Pyrolysis is a promising biomass upgrading process for the production of solid, liquid and gaseous fuels. One of the major concerns about biomass utilization is the remarkable variety of its composition in terms of both organic and inorganic matrices, affecting the pyrolysis characteristic temperatures and products yield. The effect of different alkali and earth alkali metals (AAEMs) on biomass and cellulose pyrolysis has been extensively studied, whereas only few works exist concerning the effect of AAEMs on the pyrolysis of the other two main biomass components, namely hemicellulose and lignin. Hemicellulose, which has a carbohydrate nature like cellulose, is expected to be influenced by the presence of AAEMs during the pyrolysis process. Inthis study, the impact of potassium ions (K+) on the slow pyrolysis of hemicellulose is assessed using xylan asa representative of hardwood hemicellulose. To this aim, slow pyrolysis tests, up to a temperature of 973 K using a heating rate of 7 K/min, were conducted for xylan samples loaded with K+ in different amounts. Commercial xylan was demineralized through a cation exchange resin to reduce the presence of inherentinorganics. Subsequently, the demineralized sample was doped with a controlled amount of K+ (0.3, 0.6 and1.2 wt.%). The experimental results show that doped and demineralized xylan samples exhibit different pyrolytic behaviors. The initial decomposition temperature of the doped xylan is slightly anticipated with respect to that of the demineralized xylan. Moreover, the gas production is favored at the expense of pyrolysisliquids and the evolution of the release rate of permanent gases (mainly CO2 and CO) with the temperature is significantly affected by the presence of K+.

he paper deals with the development of a modeling package aiming to a physically consistent description of atomization, dispersion and evaporation of liquid injected normally to a high-density airflow. Jet dynamics prediction has been improved by reformulating the transport equation in an eulerian frame of reference. The progressive flattening of the jet cross-section and the drag coefficient dependence on Reynolds number were also accounted for. Mass reduction due to atomization was tracked with an adapted version of the Boundary Layer Stripping model. Encouraging results were obtained by comparing predicted and measured jet trajectories, despite the inability of the BLS model to capture the capillary wave breakup mechanism also effective in crossflow atomization.

La formazione di inquinanti come il particolato fine ed ultrafine è sicuramente svantaggiata in sistemi di combustione che operano in condizioni di combustione MILD perchè gli intervalli di temperatura di lavoro deprimono le cinetiche che portano alla produzione di tali sostanze. L'utilizzo di combustibili di scarso pregio, però, può determinare la necessita di prevedere sistemi di abbattimento di particolati che in questo caso possono formarsi anche in condizioni di combustione MILD. Un processo efficiente per eliminare particolati submicronici presenti nei gas esausti prevede la condensazione di vapor d'acqua sulle particelle stesse che fungono da nuclei di condensazione. Tale processo è particolarmente vantaggioso nel caso di sistemi di combustione MILD nei quali il vapor d'acqua è utilizzato come diluente. L'attività relativa a questo pacco di lavoro ha riguardato la messa a punto di un sistema sperimentale per lo studio del processo di condensazione per l'eliminazione di particolato da correnti di gas esausti. E' stata quindi realizzata una camera in flusso laminare accessibile otticamente ed i relativi sistemi di monitoraggio e controllo. E' stata, inoltre, implementata la diagnostica ottica necessaria allo studio del processo e realizzate misure sperimentali preliminari per verificare l'affidabilità dell'impianto sperimentale al variare delle condizioni di lavoro.

Il Progetto TEPSI ha come obiettivo generale lo sviluppo di tecnologie, componenti e sistemi innovativi per promuovere la diffusione dell'idrogeno come vettore energetico per la produzione/conversione di energia nei diversi settori di applicazione a emissioni zero. Le tre linee di attività affrontano i diversi aspetti del problema: la produzione di idrogeno da fonte solare, i sistemi innovativi per lo stoccaggio efficiente di idrogeno e la fase di transizione dai combustibili fossili all'idrogeno attraverso la sua produzione e utilizzazione con sistemi a basso impatto ambientale. In questo estratto si riportano i risultati della terza annualità relativi ai seguenti obiettivi - Linea 3 Obiettivo 1: Studi teorici di base, sviluppo e ottimizzazione di modelli di simulazione dei principali componenti del sistema ZECOMIX e di sue possibili varianti Sottolinea -Studio e modellazione della combustione H2-O2 -Studio e modellazione dell'azione ripulente sulla corrente gassosa proveniente dal gassificatore Linea 3 Obiettivo 6 Sperimentazione su apparati di prova da laboratorio dei processi per la conversione energetica dell'idrogeno con cicli ad elevata efficienza Sottolinea -Sperimentazione in laboratorio sul processo di combustione dell'idrogeno

The reduction of particulate emission is among the most challenging problems in research field of pollutant control in combustion systems. This is due to very low efficiency of conventional separators, such as electrostatic precipitator, cyclone wet scrubber, in the collection of submicronic particles. To increase the diameter of fine and ultrafine particles by means of condensation of water vapor on the particles themselves seems to be a promising technique for industrial applications [1, 2]. Although several data are present in literature in the field of meteorology, cloud physics and aerosol science on nucleation and growth of droplets on foreign nuclei, a systematic analysis on dependence of such a process on parameters relevant from industrial point of view is not yet available. As a matter of a fact, temperature, partial pressure, properties of solid nuclei strongly affect the characteristic time and the efficiency of heterogeneous nucleation and the related dependence are needed for a proper design of a real abatement device. The aim of this work is to summarize the main physical relations governing the nucleation process and to describe the criteria followed in the design and set up of an experimental apparatus realized for the study of heterogeneous nucleation on submicronic particles in different conditions.

Il Progetto TEPSI ha come obiettivo generale lo sviluppo di tecnologie, componenti e sistemi innovativi per promuovere la diffusione dell'idrogeno come vettore energetico per la produzione/conversione di energia nei diversi settori di applicazione a emissioni zero. Le tre linee di attività affrontano i diversi aspetti del problema: la produzione di idrogeno da fonte solare, i sistemi innovativi per lo stoccaggio efficiente di idrogeno e la fase di transizione dai combustibili fossili all'idrogeno attraverso la sua produzione e utilizzazione con sistemi a basso impatto ambientale. In questo estratto si riportano i risultati della seconda annualità relativi ai seguenti obiettivi - Linea 3 Obiettivo 1: Studi teorici di base, sviluppo e ottimizzazione di modelli di simulazione dei principali componenti del sistema ZECOMIX e di sue possibili varianti Sottolinea -Studio e modellazione della combustione H2-O2 -Studio e modellazione dell'azione ripulente sulla corrente gassosa proveniente dal gassificatore Linea 3 Obiettivo 6 Sperimentazione su apparati di prova da laboratorio dei processi per la conversione energetica dell'idrogeno con cicli ad elevata efficienza Sottolinea -Sperimentazione in laboratorio sul processo di combustione dell'idrogeno