1,720,995 research outputs found
Monte-carlo simulation of combustion-induced percolative fragmentation of carbons
No full textPercolative fragmentation of carbon particles during combustion is modelled by means of two Monte-Carlo simulation models on a 3-D lattice: the first applies, to combustion in absence of oxygen concentration gradients within the particle; the second applies to percolative fragmentation in the intraparticle diffusion-limited combustion regime. The latter simulates oxygen diffusion and reaction by a random walk technique. Model results include the ratio of the mass rate of percolated fragments to the rate of carbon removal by combustion and percolative fragmentation, the penetration depth of oxygen in the porous matrix and the average size of fragments generated by the percolation process. The correspondence is established between model parameters and variables of the actual physical process. In particular it is shown that fragmentation rate and average fragment size and functions of a dimensionless group (the Thiele modulus) which expresses the ratio between the average size of the cavities in the lattice and the oxygen penetration depth. In absence of porosity gradients within the lattice (that is as Thiele modulus tends to 0) the rate of percolative fragmentation turns out to be smaller than that corresponding to the voidage at the percolation of the solid phase in the classical percolation theory framework. Non-uniform distribution of porosity in the lattice, like that established in diffusion limited combustion conditions, further reduces the rate of fragmentation in respect to that observed under uniform percolation conditions. In particular it is shown that fragmentation rate decreases with increasing combustion temperature, in agreement with experimental results of previous authors. The average size of fragments generated in the percolation process increases as porosity and average size of pores increase. For given lattice properties, the fragment sizes decrease when moving from uniform to diffusion limited combustion conditions, consistent with the parallel decrease of oxygen penetration depth within the lattice. © 1992 Combustion Institute
“Analisi di segnali per lo studio del meccanismo di combustione in letto fluido di combustibili liquidi”
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“A review on mixing and segregation during fluidized bed combustion of liquid fuels”
No full text51st IEA-FBC Meeting, Portoscuso (I
New Perspectives on Catalytic Hydrogen Production by the Reforming, Partial Oxidation and Decomposition of Methane and Biogas
Full text linkThe article provides a short review on catalyst-based processes for the production of hydrogen starting from methane, both of fossil origin and from sustainable processes. The three main paths of steam- and dry-reforming, partial oxidation and thermo-catalytic decomposition are briefly introduced and compared, above all with reference to the latest publications available and to new catalysts which obey the criteria of lower environmental impact and minimize the content of critical raw materials. The novel strategies based on chemical looping with CO2 utilization, membrane separation, electrical-assisted (plasma and microwave) processes, multistage reactors and catalyst patterning are also illustrated as the most promising perspective for CH4 reforming, especially on small and medium scale. Although these strategies should only be considered at a limited level of technological readiness, research on these topics, including catalyst development and process optimization, represents the crucial challenge for the scientific community
Fluidized Bed Combustion of Liquid Bio-Fuels: Application of Integrated Diagnostics for Micro-Explosions Characterization
Full text linkA novel integrated diagnostic technique has been developed for the analysis of the “regime with microexplosions” that may be established during the low-temperature (T < 800 °C) fluidized bed combustion of liquid fuels. It consists of the comparison among three analogue data series: (i) pressure signals measured in the freeboard and high-pass filtered, (ii) oxygen molar fractions measured by zirconia-based probes at two elevations in the bed and in the splash region, and (iii) video frames of the bed surface recorded and purposely worked out. The integrated technique has been applied to the combustion of biodiesel at minimum fluidization and has proven to be a valid tool to provide the fingerprints of the mechanism of the low-temperature fluidized combustion of liquid fuels. The time series generated from the measured data sets have been analyzed with the aid of the Hurst’s rescaled range analysis, the V-statistic, and the Lyapunov exponents’ evaluation. The issue of localizing micro-explosions throughout bed, bubbles, and splash zone has been tackled by the V-statistic analysis, which has proven that the location of micro-explosions is just at the bed surface when T = 650 °C and moves deeper and deeper into the bed when its temperature increased to about 800 °C. The values found
for the largest Lyapunov exponent in the time series demonstrate that the investigated system is not only
dynamic but also chaotic in its nature
Waste-derived tuff for CO2 Capture: Enhanced CO2 adsorption performances by Cation-Exchange tailoring
No full textMitigating greenhouse gas emissions through CO2 capture from industrial flue gases is imperative for addressing climate change. This article delves into the potential of natural tuff, derived from construction and demolition (C&D) waste, as an affordable and sustainable CO2 adsorbent for post-combustion capture. By tailoring the tuff structure and chemical composition through cation-exchange, the crucial role of cation type in enhancing its textural properties, particularly its microporosity and specific surface area, has been highlighted. Notably, Li- and Na-exchanges greatly enhance these properties, indicating a heightened potential for CO2 capture. The work further explores the dynamic CO2 adsorption of both untreated and modified tuff in a fixed-bed reactor under low CO2 partial pressures (< 0.2 atm), particularly examining the effects of extra-framework cation nature (Na+, Li+) and composition, and the influence of NH4+ pre-treatment. Results show that Na- and Li-exchanged tuff exhibit enhanced CO2 uptake (up to 1 mmol g−1) compared to untreated tuff (0.54 mmol g−1), with Li-exchange resulting in the highest capacity due to both superior textural properties and stronger ion-quadrupole interactions with CO2 molecules. The multi-cyclic stability of the synthesized samples has been also assessed; regardless of the specific cation-exchange type, all the samples provide stable performances over 10 consecutive adsorption/desorption cycles
Challenges, technology drivers and the role of power boilers in rapidly decarbonizing energy systems
No full textThis vision article accompanies a Special Issue of Applied Thermal Engineering dedicated to the 14th International Conference on Boiler Technology (ICBT 2022) on 'Transition technologies towards carbon neutrality and reduced environmental impacts'. The aim of the conference was to discuss recent progress, achievements and new solutions in the field of thermal power production, covering scientific research from a wide range of universities and research centres on topics relating to the design and operation of boilers and auxiliary devices for thermal power generation. This article discusses a selection of papers presented at this conference and selected for publication in Applied Thermal Engineering
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