Peripheral Fragmentation Research Articles

Investigation on axial evolution of particle group and conversion of a single coal particle in an impinging entrained-flow gasifier

Based on a bench-scale impinging entrained-flow gasifier and visualization system, the conversion of particle group and a single coal particle in the impinging-flow zone below the burner plane is investigated in-situ. The axial evolution of particle group including particle size, particle concentration, velocity field and spatial distribution is characterized with image processing algorithm and statistical method. The particle fragmentation, single particle conversion process and volatile oxidation behavior are discussed. The results indicate that the Sauter mean diameter (SMD) is distributed in 560–720 µm in all statistical regions, and the particle concentration is distributed in 20,000–360,000. With the axial downward movement of the particle group, the SMD, particle concentration and spatial distribution frequency show an overall decreasing trend. The proportion of particles ranging in the velocity interval of 0–4 m/s increases in the three impinging-flow zones, which are 85.76 %, 92.33 % and 97.88 %, respectively. The fragmentation mode of a single coal particle can be classified into central fragmentation and peripheral fragmentation. The occurrence probabilities of the two modes in the upper impinging-flow zone are more than one-third, indicating that the particles tend to be fragmented near the burner plane. The conversion of a single coal particle can be divided into heat up and pyrolysis, volatile oxidation, volatile/char oxidation and char oxidation. In the upper impinging-flow zone, less than 30 % of the particles are in volatile oxidation stage, while about 50 % of the particles are in char oxidation stage. With the axial downward movement of the particle group, the proportion of particles in char oxidation stage decreases, while the proportion of particles in volatile oxidation stage shows an opposite trend. A macroscopic description of ignition and propagation of particle volatile flame is proposed. The propagation of volatile flame between singles particles can be extended to the propagation of volatile flame within particle groups.

Dynamic modeling with experimental calibration for the syngas production from biomass fixed‐bed gasification

AbstractIn this article, a dynamic biomass gasification model was developed based on the hybrid peripheral fragmentation and shrinking‐core model. To improve the accuracy of syngas generation transient prediction, the chemical kinetic model was trained using global surrogate optimization techniques. The pre‐exponential corrections of kinetic reaction rates are calibrated under noncatalytic conditions, employing experimental transient data of syngas generation rate and compositions under different temperatures and gasifying agents. The Dynamic Coordinate search using Response surface model and the Gap Optimized Multi‐objective Optimization using Response Surfaces framework were employed as the numerical solvers for finding the global optimum solution of the pre‐exponential factors. The calibrated particle‐level kinetic models based on both single‐objective and multi‐objective approaches have been validated by experimental data in four different biomass gasification scenarios. The calibrated model shows an over 95% decrease in terms of integrated squared error (ISE)‐based model mismatch when compared with the original model.

Multi-objective optimization of an integrated biomass waste fixed-bed gasification system for power and biochar co-production

In this work, an integrated biomass waste gasification combined heat and power (CHP) system is simulated and analyzed based on a multi-scale first-principles numerical model, which consists of a 1D fixed-bed gasifier model and a 1D hybrid peripheral fragmentation and shrinking-core biomass particle model. The simulations are based on a 15kW gasification CHP system and the numerical model is validated by two different groups of experimental data, and the maximum deviation is 2.56% in syngas H2 composition prediction. A multi-objective optimization framework of the integrated biomass waste gasification CHP system is formulated that considers 3 objectives: economic benefit, greenhouse gas emission, and potential health impact caused by PM emission. The best-compromised solution from the Pareto front leads to $142.8/day economic benefit, 694.3 kg CO2eq/day mitigation, and 57.67 Singapore Pollutant Standards Index score. The impacts of the three objectives on decision variables (i.e., feedstock flowrate, feedstock moisture content, and equivalent ratio) are analyzed by investigating 21 different weighted single-objective problems.

On the modelling of the peripheral fragmentation during coal char gasification with CO2

In this paper, a novel mathematical model for the coal char gasification with CO2 is developed. This new approach considers the non-uniformity of pore size distribution, the longitudinal growth of pores due to the surface reaction between CO2 and char, the pore overlapping effect, and the peripheral fragmentation phenomenon. This phenomenon was simulated by incorporating a fragmentation criterion based on both a critical porosity and a critical porosity gradient. Model predictions were compared with experimental data taken by sieving, gas adsorption porosimetry and surface area analysis, and a remarkable agreement was obtained. It was found that critical porosity and critical porosity gradient do not depend either on the operating conditions or the initial particle size but on the initial microstructure of the coal char. Furthermore, these two parameters could not vary significantly between different coal char samples. Regarding the fragmentation, it is observed that as the diffusional limitation increases, this phenomenon takes place in even earlier stages of reaction due to the appearance of porosity gradients within the particle. It was also observed that a maximum on the specific surface area appears due to the pore overlapping phenomenon, and that under chemical control conditions, the average specific surface area that can be reached is larger than that obtained under conditions with diffusional limitations.

A hybrid peripheral fragmentation and shrinking-core model for fixed-bed biomass gasification

Biomass gasification has attracted significant interest as it generates less toxic emissions and the combustion of syngas is more efficient and easier to control than solid fuel combustions. An accurate mathematic model could be used as a cost-effective tool to understand various physical and chemical effects in the gasification process, which is essential for the optimization of thermal efficiency, economic viability and particulate matter (PM) emission reduction. In this work, we have developed a hybrid peripheral fragmentation and shrinking-core model, which considers the intra-particle heat and mass transfer, peripheral fragmentation, porosity evolution and chemical reaction kinetics. The model development involves two steps: the first step is developing a data-driven model to correlate PM emissions with operating conditions based on experimental data; the second step is coupling the PM model in the mass balance of the shrinking-core model to simulate the transient of solid phase mass loss due to peripheral fragmentation. The numerical predictions have been validated with experimental data, and the maximum deviations are 10.24%, 12.95% and 1.47% for syngas, biochar and PM emission, respectively. To the best of the authors’ knowledge, this is the first attempt to quantify syngas generation, biochar production and PM emission in a single model.

On the kinetic modeling of biomass/coal char co-gasification with steam

Co-gasification of biomass/coal blends is very promising due to many advantages. Kinetic modeling of the co-gasification process is, however, lagged behind, which is adverse to the development of the co-gasification technology. In this work, a scheme to set up kinetic models for the co-gasification of biomass/coal char blends is proposed. Based on the scheme, a kinetic model for the steam co-gasification of the blended biomass/coal char is built. The intra-particle diffusion, particle structure evolution and peripheral fragmentation are allowed for, and the effects of biomass blending ratio (BBR), gasification temperature, and steam partial pressure on the apparent co-gasfication kinetics are considered. The model prediction is compared against a series of experimental data in literature, and good agreement is achieved. It is concluded that the effects of BBR on the co-gasfication kinetics can be treated as a net increment of the coal char conversion rate, and the net increment can be well predicted by the random pore model. BBR has great impact on the particle structure and composition which greatly affect both the intrinsic kinetics and the intra-particle diffusion.

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

Whether BDs form as stars through gravitational collapse ("star-like") or BDs and some very low-mass stars constitute a separate population which form alongside stars comparable to the population of planets, e.g. through circumstellar disk ("peripheral") fragmentation, is one of the key questions of the star-formation problem. For young stars in Taurus-Auriga the binary fraction is large with little dependence on primary mass above ~0.2Msun, while for BDs it is <10%. We investigate a case in which BDs in Taurus formed dominantly through peripheral fragmentation. The decline of the binary frequency in the transition region between star-like and peripheral formation is modelled. A dynamical population synthesis model is employed in which stellar binary formation is universal. Peripheral objects form separately in circumstellar disks with a distinctive initial mass function (IMF), own orbital parameter distributions for binaries and a low binary fraction. A small amount of dynamical processing of the stellar component is accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. The binary fraction declines strongly between the mass-limits for star-like and peripheral formation. The location of characteristic features and the steepness depend on these mass-limits. Such a trend might be unique to low density regions hosting dynamically unprocessed binary populations. The existence of a strong decline in the binary fraction -- primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star forming region. It is a test of the (non-)continuity of star formation along the mass-scale, the separateness of the stellar and BD populations and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.

Swift Heavy Ion Induced Optical and Electronic Modifications of Graphene–TiO2 Nanocomposites

The effect of swift heavy ions irradiation on optical and electronic properties of chemically synthesized graphene–TiO2 nanocomposites is presented. Modification of surface properties of these nanocomposites by irradiation with three different ions and with varying fluence was analyzed by Raman spectroscopy, transmission electron microscopy, and scanning Kelvin probe microscopy techniques. Raman spectra of irradiated samples exhibit systematic changes in the characteristic peaks of both graphene and TiO2. The nanocrystallite dimension calculated from Raman peak intensity decreases with fluence, indicating the occurrence of peripheral fragmentation. Furthermore, measurement of the surface contact potential difference using scanning Kelvin probe reveals that the work function of graphene–titanium dioxide nanocomposites can be effectively increased by more than 1 eV.

CHARACTERIZING THE BROWN DWARF FORMATION CHANNELS FROM THE INITIAL MASS FUNCTION AND BINARY-STAR DYNAMICS

The stellar initial mass function (IMF) is a key property of stellar populations. There is growing evidence that the classical star-formation mechanism by the direct cloud fragmentation process has difficulties reproducing the observed abundance and binary properties of brown dwarfs and very-low-mass stars. In particular, recent analytical derivations of the stellar IMF exhibit a deficit of brown dwarfs compared to observational data. Here we derive the residual mass function of brown dwarfs as an empirical measure of the brown dwarf deficiency in recent star-formation models with respect to observations and show that it is compatible with the substellar part of the Thies-Kroupa IMF and the mass function obtained by numerical simulations. We conclude that the existing models may be further improved by including a substellar correction term that accounts for additional formation channels like disk or filament fragmentation. The term "peripheral fragmentation" is introduced here for such additional formation channels. In addition, we present an updated analytical model of stellar and substellar binarity. The resulting binary fraction and the dynamically evolved companion mass-ratio distribution are in good agreement with observational data on stellar and very-low-mass binaries in the Galactic field, in clusters, and in dynamically unprocessed groups of stars if all stars form as binaries with stellar companions. Cautionary notes are given on the proper analysis of mass functions and the companion mass-ratio distribution and the interpretation of the results. The existence of accretion disks around young brown dwarfs does not imply that these form just like stars in direct fragmentation.

The influence of gasification reactions on char consumption under oxy-combustion conditions: Effects of particle trajectory and conversion

The effects of char gasification reactions during oxy-combustion of pulverized coal are dependent on the boundary conditions and are not fully understood. In this study, a CFD simulation of lignite coal combustion in a pilot-scale oxyfuel test facility with a 29% oxygen feed are used to determine representative regions (pre-flame, flame, and post-flame) in which char particles are burned. Coal particle trajectories are analyzed to extract representative time-dependent boundary conditions to which char particles are exposed as they traverse the furnace. These realistic boundary conditions are then employed in a detailed, single particle char consumption model to evaluate the influence of the local environment and char conversion on the importance of the gasification reactions to the overall rate of char consumption, using apparent initial reaction rates of char oxidation and gasification in-line with the literature estimates. In the pre-flame region, gasification reactions are of little importance; in the flame region char gasification reactions should not be neglected; while in the post-flame regions, the impact of gasification depends on the particle’s trajectory. When gasification is non-negligible, its significance depends on the particular char’s physical, and especially kinetic, properties. As conversion proceeds, gasification reactions, when significant, can alter the location within the particle where char consumption occurs, further affecting the rate of char consumption. Their impact can induce structural changes that may accelerate conversion via peripheral fragmentation.

Golgi apparatus fragmentation as a mechanism responsible for uniform delivery of uroplakins to the apical plasma membrane of uroepithelial cells

The GA (Golgi apparatus) has an essential role in membrane trafficking, determining the assembly and delivery of UPs (uroplakins) to the APM (apical plasma membrane) of superficial UCs (uroepithelial cells) of urinary bladder. UPs are synchronously and uniformly delivered from the GA to the APM by DFVs (discoidal- or fusiform-shaped vesicles); however, the mechanism of UP delivery is not known. We have used the culture model of UCs with the capacity to undergo terminal differentiation to study the process of uniform delivery of DFVs to the APM and to elucidate the mechanisms involved. By three-dimensional localization using confocal microscopy of immunofluorescence-labelled GA-related markers [GM130 (cis-Golgi matrix protein of 130 kDa), GS15 (Golgi Snare 15 kDa), GS28 and giantin], uroepithelial differentiation-related markers (UPs), MTs (microtubules; α-tubulin) and intermediate filaments [CK7 (cytokeratin 7) and CK20], we found that in non-differentiated, UP-negative UCs the GA is mostly organized as a single ribbon-like structure close to the nucleus, whereas in differentiated, UP-positive UCs the GA is fragmented and spread almost through the entire cell. The FRAP (fluorescence recovery after photobleaching) experiments on the UCs transfected with GalT (trans-Golgi/TGN enzyme β1,4-galactosyltransferase) fused to fluorescent protein showed that Golgi-resident enzyme cycles freely within ribbon-like GA but not within fragmented GA. By CLEM (correlative light-electron microscopy), we examined the GA fragments in cells expressing UPs. We found that GA fragments are fully functional and similar to the GA fragments that are formed after nocodazole treatment. Furthermore, we demonstrated that the reorganization of GA into a fragmented form is associated with the impairment of the MT organization in the basal, central and subapical cytoplasm and the accumulation of intermediate filaments in the apical cytoplasm that could affect the kinetics of MT star leading to the peripheral fragmentation of the GA in the differentiated UCs. The fragmentation of the GA and the subsequent spreading of GA to the cell periphery represent one of the key events that promote the uniform delivery of UPs over the entire APM of differentiating UCs and thus are of major importance in the final proper formation and maintenance of the blood-urine barrier.

Impact of peripheral fragmentation on the steam gasification of an isolated wood charcoal particle in a diffusion-controlled regime

This study focuses on the effect of peripheral fragmentation during gasification of an isolated wood charcoal particle in the regime of diffusional limitations. In fact, all the models available in the literature fail to reproduce the specific changes in biomass charcoals for which conversion increases quasi linearly versus time, whatever the particle size. We assumed this discrepancy is partly due to the fragmentation phenomenon, i.e. the detachment of fragments from the surface of the particle, which is not usually taken into account in models. The classical assumption in percolation models is a critical value of porosity beyond which fragmentation occurs. We compared our model results with experimental data. We demonstrated that in the diffusion-limited regime, the direct extrapolation of such a method to a continuum model is not satisfying. A new criterion of fragmentation based on a critical porosity and a critical porosity gradient is proposed which considerably improves modelling of gasification charcoal particles.

Peripheral fragmentation of relativistic nuclei 11B in nuclear track emulsion

Data obtained from a nuclear track photoemulsion exposed to a beam of 11B nuclei with a momentum of 2.75 GeV/c per nucleon are reported. Peripheral interactions where the total charge of particles emitted within the forward cone of relativistic fragmentation is equal to the charge of the projectile nucleus are analyzed to study the clustering of the 11T nucleus. It is found that the three-body breakup of 2 + 2 + 1 charge configuration is a leading process. Tritons are revealed to play a crucial role in the most peripheral interactions of this type. Events interpreted as charge exchange of the 11B nucleus to excited states of the 11C* nucleus above the nucleon-coupling threshold were observed for the first time. Prospects for studying the 11C nucleus are discussed.

MODES OF REPRODUCTION IN RECENT AND FOSSIL CUPULADRIID BRYOZOANS

Abstract: Cupuladriid cheilostome bryozoans can make new colonies both sexually and asexually. Sexual (aclonal) colonies are derived from larvae while asexual (clonal) colonies result from the fragmentation or division of larger colonies. A number of specialised morphologies exist which either enhance or discourage clonality, and cupuladriids preserve these in their skeletons, meaning that it is possible to count the abundances of individual modes of reproduction in fossil assemblages, and thus measure the mode and tempo of evolution of life histories using fossil colonies. In this paper we categorise, illustrate and describe the various clonal and aclonal methods of propagation in cupuladriids through the Cenozoic. Sexual reproduction is the only aclonal method of propagation, while four clonal methods are described comprising: (1) mechanical fragmentation, (2) autofragmentation, (3) colonial budding and (4) peripheral fragmentation. The processes involved in each are discussed and we explain how their prevalence can be measured in the fossil record using preservable morphologies. Compiling a record of the occurrence and distribution of the various modes of propagation through time and space we discover a general trend of evolution towards more complex modes in all three cupuladriid genera, but a geologically recent extinction of some modes of propagation that has left the present‐day assemblage relatively depauperate. We see striking similarities in the general timing of expansion of modes of reproduction between the two most important genera, Cupuladria and Discoporella, although it is clear that Discoporella evolved a much wider range of special morphologies either to enhance or to discourage clonality than did Cupuladria.

Peripheral fragmentation of 8B nuclei in nuclear emulsion at an energy of 1.2 GeV per nucleon

The results obtained by studying the charge topology of fragments produced in the peripheral dissociation of relativistic 8B nuclei in emulsion are presented. Fifty-five events of the peripheral dissociation of a 8B nucleus in events where there was no production of target-nucleus fragments and mesons (“white stars”) were selected. A leading contribution of the 8B → 7Be + p mode, which has the lowest energy threshold, was revealed on the basis of these events. Information about the branching ratios for dissociation modes characterized by a higher multiplicity was obtained. The dissociation of the 7Be core in 8B bears resemblance to the dissociation of a free 7Be nucleus. The transverse-momentum distributions of fragments originating from the 8B → 7Be + p dissociation mode were obtained. For these distributions, a small mean value of 〈P*T〉 = 52 ± 5 MeV/c in the c.m. frame suggests a low binding energy of the outer proton in the 8B nucleus. An indication of a strong azimuthal correlation of the fragments 7Be and p was found.

Experimental and numerical study of steam gasification of a single charcoal particle

The present work deals with a study coupling experiments and modeling of charcoal gasification by steam at large particle scale. A reliable set of experiments was first established using a specially developed “macro-TG” apparatus where a particle was suspended and continuously weighed during its gasification. The main control parameters of a fixed-bed process were modified separately: steam gasification of beech charcoal spheres of different diameters (10 to 30 mm) was studied at different temperatures (830 to 1030 °C), different steam partial pressures (0.1 to 0.4 atm H 2O), and different gas velocities around the particle (0.09 to 0.30 m/s). Simulations with the particle model were performed for each case. Confrontations with experimental data indicate that the model predictions are both qualitatively and quantitatively satisfactory, with an accuracy of 7%, until 60% of conversion, despite the fact that the phenomena of reactive surface evolution and particle fracturing are not well understood. Anisotropy and peripheral fragmentation make the end of the process difficult to simulate. Finally, an analysis of the thermochemical situation is proposed: it is demonstrated that the usual homogeneous or shrinking core particle models are not satisfying and that only the assumption of thermal equilibrium between the particle and the surrounding gas is valid for a model at bed scale.

Four-body distorted-wave theory for halo excitations in peripheral fragmentation reactions

A microscopic approach to breakup into the low-energy continuum of Borromean two-neutron-halo nuclei is developed by quantum mechanically taking into account both Coulomb and nuclear dissociation. The crucial role of both elastic and inelastic fragmentation is demonstrated for 6He breakup on C and Pb targets at intermediate energies in kinematically complete experiments. For the first time, recent GSI experimental data are analyzed quantitatively, and a rich and complex interplay of reaction mechanisms and low-lying halo excitations is revealed.

A generalised dynamic model for char particle gasification with structure evolution and peripheral fragmentation

A generalised model for the prediction of single char particle gasification dynamics, accounting for multi-component mass transfer with chemical reaction, heat transfer, as well as structure evolution and peripheral fragmentation is developed in this paper. Maxwell–Stefan analysis is uniquely applied to both micro and macropores within the framework of the dusty-gas model to account for the bidisperse nature of the char, which differs significantly from the conventional models that are based on a single pore type. The peripheral fragmentation and random-pore correlation incorporated into the model enable prediction of structure/reactivity relationships. The occurrence of chemical reaction within the boundary layer reported by Biggs and Agarwal (Chem. Eng. Sci. 52 (1997) 941) has been confirmed through an analysis of CO/CO 2 product ratio obtained from model simulations. However, it is also quantitatively observed that the significance of boundary layer reaction reduces notably with the reduction of oxygen concentration in the flue gas, operational pressure and film thickness. Computations have also shown that in the presence of diffusional gradients peripheral fragmentation occurs in the early stages on the surface, after which conversion quickens significantly due to small particle size. Results of the early commencement of peripheral fragmentation at relatively low overall conversion obtained from large a number of simulations agree well with experimental observations reported by Feng and Bhatia (Energy & Fuels 14 (2000) 297). Comprehensive analysis of simulation results is carried out based on well accepted physical principles to rationalise model prediction.

Direct Experimental Evidence for Strong Admixture of Different Parity States in11Li

Peripheral fragmentation of a 287 MeV/nucleon beam of the halo nucleus 11Li incident on a carbon target has been studied in a fragment-neutron coincidence experiment. The momentum distribution of the 10Li fragments gives access to the momentum distribution of the removed neutron in 11Li. From the shape of the distribution, the (1s1/2)2 contribution to the mixture of (1s1/2)2 and (0p1/2)2 components in the ground-state wave function was determined to be (45±10)%. The angular correlation between the knocked out neutron and the one from the decay of 10Li shows a skew distribution signaling interference of these two different parity states.Received 9 December 1998DOI:https://doi.org/10.1103/PhysRevLett.83.496©1999 American Physical Society

Fragment-neutron correlations in peripheral fragmentation of halo nuclei

Studies of nuclei far off the line of stability are one of the main topics in nuclear structure physics. The search for states with spatially extended low-density matter distributions, so-called “halos”, found predominantly in light neutron-rich nuclei is of central importance. Halo-breakup experiments were performed in complete kinematics with relativistic secondary beams of energies of 0.2–0.4 GeV/u at GSl. For the examples of the two-neutron halo nuclei 6He and 11Li results of angular, energy and momentum correlation measurements after breakup into a core fragment and valence neutrons are given and single-particle ground-state properties and large low-lying multipole strength near the threshold for particle emission will be discussed.