1,721,027 research outputs found
110th Anniversary: MILD Combustion of Liquid Hydrocarbon-Alcohol Blends
Full text linkAmong the various low NOx combustion technologies, MILD combustion combines low pollutant emissions, combustion stability and efficiency, fuel flexibility, and noise reduction through a high preheating of the combustion chamber coupled with a massive exhaust gas recirculation at high turbulence level. In this work, the sustainability of MILD combustion for liquid hydrocarbon-alcohol blends (as possible constituents of surrogate fuels representing the behavior of blends of fossil fuels and biofuels) has been investigated experimentally using a dual-nozzle laboratory-scale burner. Several hydrocarbon-alcohol blends have been investigated to identify the regions (in the furnace temperature vs dilution ratio space) where MILD combustion can be sustained with low NOx and CO emissions. It has been found that the MILD combustion conditions of the various liquid fuel blends investigated differ slightly one to each other and are quite similar to that of the hydrocarbons without any oxygenated species. This means that a MILD combustion burner shows a large flexibility in terms of fuel properties, therefore creating a suitable environment for NOx and CO depression also for fossil fuels-biofuels blends
Experimental design of topological curves to safely optimize highly exothermic complex reacting systems
No full textStrongly exothermic solution homopolymerizations are a class of chain reactions particularly difficult to be optimized from both a safety and a productivity viewpoint. Particularly, lots of side undesired reactions (e.g., backbiting, propagation of tertiary radicals, chain transfer to monomer or solvent, etc.), which affect the selectivity with respect to the desired product, and relevant mass and heat transfer problems, due to the increasing system viscosity, take place during such syntheses. Under these unavoidable operating conditions, it is difficult to employ theoretical procedures that are able to safely optimize the analyzed process, because the development of a reliable mathematical model is often not affordable or too time-consuming. In this work, it is shown that the topological criterion theory and its related optimization procedure can be used to optimize experimentally (through a dedicated set of isoperibolic reaction calorimetry tests) a complex reacting system even if its reaction scheme and all information about the kinetics are not available
Numerical and experimental analysis of NO emissions from a lab-scale burner fed with hydrogen-enriched fuels and operating in MILD combustion
No full textAn experimental and computational investigation of a lab-scale burner, which can operate in both flame and MILD combustion conditions and is fed with methane and a methane/hydrogen mixture (hydrogen content of 60% by vol.), is carried out. The modelling results indicate the need of a proper turbulence/chemistry interaction treatment and rather detailed kinetic mechanisms to capture MILD combustion features, especially in presence of hydrogen. Despite these difficulties, Computational Fluid Dynamics results to be very useful, as for instance it allows evaluating the internal recirculation degree in the burner, a parameter which is otherwise difficult to be determined. Moreover the model helps interpreting experimental evidences: for instance the modelling results indicate that in presence of hydrogen the NNH and N(2)O intermediate routes are the dominant formation pathways for the MILD combustion conditions investigated. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved
Modelling of indoor air pollutants dispersion: New tools
Full text linkVentilation systems are used for create a thermally comfortable environment and good indoor air quality. It is therefore essential to have adequate tools for predicting the performance of these systems. Among the various approachs, the computational fluid dynamics could be a useful tool for the design of the ventilation system. When dealing with pollutants dispersion problems, a steady state averaged simulation can be misleading because it is not able to properly predict and model peak concentrations, which can be relevant even if temporary. An interesting approach is the use of LES (Large Eddy Simulations) simulations to obtain a better description of concentrations oscillations. In this framework, the aim of this work is the validation of simulation carried out using the FDS (Fire Dynamic Simulator) software with an actual case study, already studied with a mock-up. Secondly, two new configurations of the ventilation system are proposed, in order to stress the capacity of the software to describe complex and different features, classical of HVAC (Heating, Ventilation and Air Conditioning) systems. Interesting conclusions about efficiency are drawn from the comparison, highlighting the potentiality of the software
Reaction Runaway as a Domino Effect of Pool Fire Engulfing an Ethoxylation Reactor
Full text linkIn industrial safety, engulfing pool fires can cause damages and collapse of process vessels with catastrophic consequences. This work investigates the ethoxylation of 1-dodecanol as a case-study with a multiscale approach able to analyse scenarios of runaway triggered by a pool fire engulfing the reactor. The aim is to understand whether and when the cooling power of the external heat exchanger can prevent dangerous temperature build-up in the chemical reactor
Amino-functionalized magnetic nanoparticles for CO2 capture
Full text linkCO2 accumulation is inducing an effect of global warming. Adsorption using solid sorbents is proving as an effective strategy for CO2 capture and reuse. The aim of this study was to develop amino-functionalized magnetic nanoparticles by depositing various amines through co-precipitation or impregnation-sonication. Structural characteristics were studied through SEM, BET and XRD analyses, evidencing coarse particles with low crystallinity and surface areas of 100–150 m2 g−1, while FT-IR confirmed CO2 interacting with substrate. The load of functional group, particles stability, and CO2 sorption capacity were assessed through elemental and thermogravimetric analysis. It was found that loads of functional groups ranging from 1.6 to 6.1 wt.%. were deposited, and most samples showed sound stability up to 100°C. Sorption capacities were in the range 0.2–1.5 g gNH2−1, the highest being 1.46 g gNH2−1 for ɛ-aminocaproic acid. Such sample also exhibited good recyclability, with a performance drop of 11% after many cycles. CO2 uptake decreased with increasing temperature in the range 25–45°C, suggesting a chemical bond between CO2 and amines. Amino functionalized particles could thus be an interesting solution for CO2 capture and utilization thanks to fast kinetics, recyclability, and ease of separation
Jet fires and reaction runaway interaction: A multiscale approach
Full text linkIn industrial safety, large engulfing jet fires can cause damages and collapse of process vessels with catastrophic consequences; however, even smaller jet fires can be extremely dangerous due to their ability to induce hazardous conditions when chemical reacting systems are involved. This work investigates the ethoxylation of 1-dodecanol as a case-study to investigate the potentialities of a multiscale approach able to analyse scenarios of accidental impingement on a chemical reactor involving a jet fire. In particular, the investigated system was a Venturi tower reactor, where the reacting fluid is pumped, cooled via an external heat exchanger and sprayed from the top of the reactor together with ethylene oxide. The aim is to understand if and when the cooling power of the external heat exchanger can prevent dangerous temperature build-up in the chemical reactor. The multiscale approach used in this work involves a series of mathematical simulations aimed at evaluating the effects of different jet fires in terms of heat flux entering the Venturi reactor impinged by a jet fire. These simulations were carried out using a mathematical model developed in the framework of computational fluid dynamics (CFD). The results of such simulations were used to carry out a parametric study with a 0D model able to foresee the dynamic behaviour of the reactor impinged by the jet fire. Preliminary results confirmed the possibility of linking jet fires characteristics with the time available before dangerous conditions in the Venturi reactor occur, therefore allowing for making an estimation of the time available for activating proper mitigation measures
A mathematical model for the prediction of the KSt for metallic dusts as a function of the particle size distribution
Full text linkFor several years, dust explosions have been one of the major causes of industrial accidents, spanning from metalworking to pharmaceuticals sectors. In accordance with the latest Chemical Safety Board (CSB) investigations, three out of four dust explosions in the United States involved metallic dusts (iron, titanium, zirconium and aluminum). Many chemical processes involve metal powders for their exceptional mechanical, optical and catalytic properties, such as the production of plastics, rubber, paints, coatings, inks, pesticides, detergents and even drugs. The severity of a dust explosion can be defined using experimental parameters such as the maximum explosion pressure (pmax), the maximum rate of pressure rise ((dp/dt)max) and the deflagration index (Kst), which are employed to predict the consequences of a dust explosion for a given scenario. Among these parameters, the deflagration index plays a fundamental role, as it is used for the design of deflagration nozzles aimed to protect industrial equipment and silos from internal dust explosions. The purpose of this work is to develop a mathematical model able to predict the Kst value of metal powders as a function of chemical-physical data and the particle size distribution (DD50 was used as global information). The model structure is based on the writing and resolution of the material and energy balance equations on the single dust particle, also estimating the contribution of oxygen diffusion which, in the case of metal powders, greatly depends on both tortuosity and porosity. The results well agreed with experimental data, providing the basis for the development of more detailed models
Topological criteria to safely optimize hazardous chemical processes involving consecutive reactions
No full textSafe operating conditions, for strongly exothermic chemical systems involving multiple reactions, are particularly critical to be obtained, because of the complex interactions between selectivity and safety constraints. In this work, new criteria, which are useful for isoperibolic semibatch processes involving consecutive reactions and based on the topology of a particular phase space, are presented. Such criteria are able to detect both the runaway boundary and the so-called “quick onset, fair conversion, smooth temperature profile” (QFS) operating region by performing a topological analysis of the phase space of the system of ordinary differential equations (ODEs) that describe the analyzed process. Moreover, a safe optimization procedure, the objective of which is to obtain the optimum values both of the dosing time of the dosed reactant and the initial reactor temperature, based on such criteria, has been developed. Finally, such a set of optimum operating parameters has been validated through a comparison with experimental data from published literature
Application of a Gaussian model to simulate contaminants dispersion in industrial accidents
No full textThe increase of the industrial production and the development of new processes led to the necessity of better regulations of activities concerning potential risks for human health and environment. Accomplishing such purposes requires studies on both the chemistry of the involved phenomenon and the dispersion mechanism in the surrounding environment. While the chemistry of reaction can be determined at small scale via laboratory experiments and models, the dispersion in the environment is an extremely complex phenomenon to model, because it is strongly affected by the atmospheric conditions. Several models with the purpose of simulating pollutants dispersion were developed (Gariazzo et al., 2012; Alemayehu et al., 2015; Fang et al., 2018); among those, Gaussian models found many applications in safety engineering, due to both their effectiveness and relatively low computational costs. The US-EPA recommends the use of the Gaussian model AERMOD for the simulation of dispersions within 50 km from the emission source. It is important to underline that most of these models were developed with the aim to simulate the dispersion of continuous emissions such as those from industrial chimneys. Such systems can be assumed to work under steady-state conditions, since they are supposed to work for a long time. Nonetheless, industrial accidents, which can have a severe impact on people and environment, generally occur at a relatively small time scale, thus their dispersion has not yet reached the steady state conditions. In this work, we developed a modified non-steady-state Eulerian Gaussian model able to simulate the dispersion of contaminants produced by an industrial accident, which is hypothesized to be a point source. The model requires as input data time-dependent meteorological conditions and topographic information of the site, concerning: the source, physical properties of the pollutant, emission height and release temperature. The proposed model was applied to the 2,3,7,8-Tetrachlorodibenzodioxin (TCCD) dispersion after the Seveso accident (1976) near the source (radius of about 4 km). Results highlighted a good agreement with available literature experimental data
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