Particuology最新文献

To investigate the non-uniform distribution of different gases passing through the parallel cyclones, experiments were conducted on a circulating fluidized bed (CFB) equipped with six asymmetrical cyclones. A multi-tracer gas method was used, with CO, O₂, and CO₂ chosen to represent gases with different properties in the flue gas at the inlets of the cyclones. The uniformity of multi-gas distribution was evaluated by measuring the concentration deviations of each tracer gas passing through individual cyclones. The results indicate that the concentrations of multi-tracer gases are higher in the middle cyclone among the three, which are located on the tracer gas injection side during the test of single-side secondary air (SA) tracing. The maximum concentration deviation of tracer gases is for CO₂, while the minimum is for CO. At the three cyclone inlets on the opposite side, the tracer gas with higher density exhibits a more uniform distribution, and the gas uniformity decreases as the density decreases. The effects of superficial velocity, SA ratio, bed inventory, and tracer gas injection region on the uniformity of gas distribution were studied. The results show that superficial velocity and SA ratio primarily affect the uniformity of higher density gases, while bed inventory has a greater influence on lower density gases. The gas distributions are most non-uniform, especially for CO₂, when the tracer gas injection region is near the rear wall closer to the induced draft fan during the test of regional SA tracing.

Considering the strong dependence of agglomerate characteristics on various operating parameters, this study employs the control variable methodology (CVM) and response surface methodology (RSM) to investigate the influence of multi-factor interactions on particle growth during top-spray fluidized bed agglomeration. First, CVM is conducted to assess the effects of individual operating parameters on the agglomerate properties, such as mean particle size, relative width, and sphericity. Then, the interactive relationship between these input variables and the quality attributes of the process is investigated using RSM. The results show that the mean particle size increases with the increase of binder viscosity and spray rate, while it decreases with the increase of fluidization gas velocity and inlet gas temperature. The relative width of the particle size distribution increases with the spray rate, binder viscosity, and fluidization gas velocity, and hardly changes with the inlet gas temperature. The mean particle size is more sensitive to the binder spray rate at a lower level of fluidization gas velocity or a higher level of inlet gas temperature. The fluidization gas velocity corresponding to the maximum D₅₀ changes when the binder viscosity and binder spray rate are at different levels.

Regarding sugar and salt crystallization with large single crystals, the agglomerate thermodynamics and geometric morphologies, not the dynamics, dominate the particle size distribution (PSD). To consider this issue, a PSD design model is proposed for limited large crystal agglomeration. In this model, the agglomeration thermodynamic criticality is determined by estimating the adhesion and dispersion forces between single crystals. The geometric agglomerate morphologies are described by corresponding single crystal units stacking with porosity. By seed well-controlled of population, the key parameters of PSD (D01, D50 and D99) are precisely designed. For erythritol, the model design accuracies are 92%–99% in the 1.2 L and 10 L crystallizers, indicating that it can design PSD at various crystallization scales. Concerning the general research attention to microcrystal agglomeration kinetics (mostly active pharmaceutical ingredients), this model effectively guides the sugar and salt PSD design with limited large crystal agglomeration.

This study investigates the adverse effects of fine clay minerals on low-rank coal (LRC) flotation. Zeta potential analysis, X-ray photoelectron spectroscopy, flotation experiments, and the particle-bubble attachment index (PBAI) were employed to assess these effects. Results indicate that quartz and chlorite particles are more prevalent in the flotation concentrate than kaolinite and montmorillonite, likely due to their preferential adsorption of flotation collectors, which inhibits the hydrophobicity of the LRC surface. Montmorillonite, however, exhibits greater adhesion to LRC surfaces due to its positive charge. Extended DLVO theoretical analysis reveals that polar surface interaction energy is a primary driving force in coal-mineral interactions and is crucial in overcoming the energy barrier posed by electrostatic double-layer forces. The impact of clay minerals on LRC flotation is highly dependent on clay type.

In this study, the discrete element method was combined with physical experiments to examine the capsule filling practice in the hot-isostatic-pressing process and to study the densification of spherical particles in a three-way pipe capsule for offshore engineering under mechanical vibration conditions. The effects of vibration parameters—such as the vibration time, vibration frequency, vibration amplitude, rolling friction coefficient, sliding friction coefficient, recovery coefficient, and other particle properties—on the filling density were analyzed. The results showed that the packing density in the three-way capsule could be increased considerably using a vibration frequency of 40 Hz and a vibration amplitude of 2.5 mm. The contact form between particles in the vibration-assisted mold-filling process was determined and the particle velocity field, compression force, and coordination number under a single harmonic vibration period were analyzed. The real-time motion of the particles at the micro level was visualized, and the mechanism of the mechanical vibration effect on mold filling and densification was explored. The distribution and evolution of the coordination number indicated that the distribution of the filling density was uneven, and that the change in the coordination number of particles at the bottom exhibited no major response to the vibration.

Wet-milling in liquid-solid system can achieve ultra-fine mechanical dissociation of solid wastes with low energy consumption, thereby efficiently improving the potential pozzolanic reactivity. However, the wet-milling kinetics of ultrafine dissociation in liquid-solid system has not been fully investigated. This paper systematically investigates the wet-milling kinetics of fly ash (FA). Results showed that before wet-milling of FA for 360 min, no agglomeration effect was observed. The particle dissociation of FA during wet-milling can be divided into three stages: rapid dissociation, slow dissociation and stabilization. The evolution process of particle size distribution during wet-milling is consistent with the Rosin-Rammler-Bennet distribution. Both the particle uniformity coefficient and fractal dimension showed highly positive linear correlation with the strength activity index of wet-milled FA. The grey correlation analysis showed that FA particles between 1.1 and 3.1 μm had the greatest impact on both the early and late strength activity index. Simultaneously, D₁₀ of wet-milled FA has the largest impact on strength activity index at each age, while D₁₀₀ has the least impact. Therefore, D₁₀ and proportion of particles in 1.1–3.1 μm can be an important basis for judging the reactivity of wet-milled FA as ultrafine supplementary cementitious materials.

The Jahn-Teller effect and the dissolution of Mn are significant factors contributing to the capacity degradation of spinel LiMn₂O₄ cathode materials during charging and discharging. In this study, Mo⁶⁺-doped polycrystalline octahedral Li_1.05Mn_2-xMo_xO₄ (x = 0, 0.005, 0.01, 0.015) cathode materials were prepared by simple solid-phase sintering, and their crystal structures, microscopic morphologies, and elemental compositions were characterized and analyzed. The results showed that the doping of Mo⁶⁺ promoted the growth of (111) crystalline facets and increased the ratio of Mn³⁺/Mn⁴⁺. The electrochemical performance of the materials was also tested, revealing that the doping of Mo⁶⁺ significantly improved the initial charge/discharge specific capacity and cycling stability. The modified sample (LMO-0.01Mo) retained a reversible capacity of 114.83 mA h/g with a capacity retention of 97.29% after 300 cycles. Additionally, the doping of Mo⁶⁺ formed a thinner, smoother SEI film and effectively inhibited the dissolution of Mn. Using density-functional theory (DFT) calculations to analyze the doping mechanism, it was found that doping shortens the Mn-O bond length inside the lattice and increases the Li-O bond length. This implies that the Li⁺ diffusion channel is widened, thereby increasing the Li⁺ diffusion rate. Additionally, the modification reduces the energy band gap, resulting in higher electronic conductivity.

This study aims to conduct a sensitivity analysis of closure models and modeling parameters for the Dense Discrete Phase Modeling (DDPM) approach in order to investigate the hydrodynamics of a 3D lab-scale Tapered Fluidized Bed (TFB). The closure models and model parameters under investigation include the gas-solid drag force, viscous models, particle-particle interaction models, restitution coefficient, specularity coefficient, and rebound coefficient. The primary objective of this sensitivity analysis is to optimize the numerical model's performance. The numerical results, in terms of axial and lateral Solid Volume Fraction (SVF) profiles obtained from the sensitivity analysis, indicate that the drag force and restitution coefficient significantly influence the hydrodynamics of the TFB. Properly selecting these parameters could result in the improved performance of the numerical model. However, the sensitivity of turbulence models, particle-particle interaction models, specularity coefficient, and rebound coefficient has a lesser impact on the hydrodynamics results. This work concludes with the recommendation of a set of closure models and modeling parameters that offer the most accurate prediction of the hydrodynamics of the TFB.

The influence of ammonia and Brown gas injection on the iron ore sintering characteristics was explored through sintering pot experiments based on biochar substitution to increase biochar substitution proportion and reduce fossil energy consumption. By dividing the high-temperature stage of the sintering bed, the heating rate and cooling rate were calculated, and the reasons for poor sintering quality under a high biochar substitution ratio were explored. The results showed that under the 40% biochar substitution ratio, the cooling rate of the sintering bed significantly increased, the high-temperature duration time was short, and the sintering quality deteriorated severely. Additional injection of 0.5–1% vol ammonia or 1–2% vol Brown gas can reduce the cooling rate, prolong the high-temperature duration, and optimize the sintering quality. Based on 1% vol ammonia or 2% vol Brown gas injection, reducing the proportion of biochar with equal calorific value further increases the sintering comprehensive index, which means that using 1% vol ammonia or 2% vol Brown gas injection to assist sintering can reduce the proportion of coke usage to 60%, while the proportion of biochar substitution is 33.76% and 32.47%, respectively. The research results provide an effective solution for low-carbon sintering.

A double-tube cooler with liquid-solid circulating fluidization operation and corresponding parameter measuring system are developed to avoid fouling of inner walls of heat exchange tubes in a cryogenic temperature external cooler of ammonium chloride solution in soda ash production. Wall-scaling prevention performance of the cooling process is experimentally evaluated using convection and overall coefficients, enhancement factor, wall temperature and fouling resistance. Effects of different volume fractions of added particles, particle size, superficial liquid velocity, and cooling medium temperature on heat transfer are examined. Under present conditions, convection coefficient of liquid-solid flow inside the tube of external cooler is higher than that of the liquid phase flow, increased by 0.7–2.8 times, enhancing cooling performance obviously. Convection coefficient initially increases and then decreases as the volume fraction of added particles increases, reaching its maximum value at a volume fraction of 2.0%. The wall-scaling prevention effect of glass beads mainly depends on the volume fraction of added particles; optimal anti-fouling effects are achieved when adding particles at a volume fraction of 2.0%, regardless of changes in superficial liquid velocity or cooling medium temperature. This study lays a foundation for industrial applications of this new technique of fluidized bed external coolers.