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Shaft injection of reducing gas into ironmaking blast furnaces (BF) helps mitigate BF carbon footprint. However, its effectiveness relies on the interaction between shaft-injected gas (SIG) and other phases. This paper numerically studies shaft gas injection operations based on a 380-m3 industrial BF. A recently developed three-dimensional process model has been adopted to do so. This model is extended to track SIG and hearth-generated gas (HGG), define SIG penetration, and quantify the respective contributions of the two gases to BF performance. After validation, the model is applied to study the effects of three variables related to SIG penetration into the particle bed: SIG flow rate, shaft tuyere number, and horizontal cavity depth. The detailed analysis of flow and thermochemical behaviors shows that increasing the SIG flow rate increases the gas penetration and indirect reduction rate by SIG and lifts the cohesive zone. However, it impedes the indirect reduction reaction by HGG and increases the bed pressure. These effects collectively identify an optimum SIG flow rate. In addition, as the shaft tuyere number or horizontal cavity changes, the SIG penetration zone size changes oppositely in radial and circumferential directions, leading to similar total penetration zone sizes. Consequently, these two variables can limitedly improve BF performance, especially compared with the effect of SIG flow rate. The results suggest that the model offers convenience for exploring the shaft gas injection technology.

Solid-state lithium batteries (SSLBs) are promising energy-storage devices.

PTFE-filled textured surfaces were impregnated with the dopamine dipping solution to improve their tribological performances. Ball-on-disc wear experiments were conducted to compare tribological properties of three surfaces: the textured surface, filled textured surface and modified filled textured surface. The worn surfaces, wear debris, and shedding areas of the PTFE were measured, and shear strength between the PTFE block and medium carbon steel after impregnation modification was analysed. Experimental results showed that compared with textured surfaces, filled textured surfaces and modified filled textured surfaces had lower friction coefficient values and cross-sectional areas of wear scars. Compared with the filled textured surface, the modified filled textured surface reduces filled gaps by 63.5% and the shedding ratio of the PTFE within dimples by 63.2%. The research results demonstrate that tribological performances of the filled textured surface can improve after impregnation modification. Polydopamine can react to covalent-noncovalent interaction with PTFE and medium carbon steel. Polydopamine acts as a binder to improve the bonding strength between the PTFE and the inner wall of dimples. Polydopamine can reduce the shedding ratio of the PTFE and maintain the antifriction function of the PTFE in dimples.

Hydrogen injection is a promising technology currently under development to reduce CO2 emissions in ironmaking blast furnaces (BFs). Therefore, hydrogen BF is studied by a recent process model based on computational fluid dynamics (CFD). It focuses on the effect of peripheral opening extent (POE), which represents the coke amount near the furnace wall. The simulations consider a 380 m3 BF operated with hydrogen injection through both shaft and hearth tuyeres. The overall performance of the BF is analyzed in terms of the inner states. It shows that increasing POE hinders the pre-reduction and pre-heating roles of shaft-injected hydrogen (SIH) but improves the CO indirect reduction rate. An optimum peripheral opening extent can be identified to achieve a maximum hot metal (HM) temperature, relatively low bed pressure, and good gas utilization. The interaction between SIH flow rate and burden distribution is also quantified. It shows that the increase in SIH flow rate slows down the CO indirect reduction rate but enhances the H2 indirect reduction rate. These opposite trends account for the less variation of HM temperature with POE as the SIH flow rate increases. This variation becomes trivial at relatively large SIH flow rates and small POEs. Overall, the POE affects the cohesive zones more than the SIH flow rate. However, under the conditions considered, both variables cannot significantly improve the penetration of the shaft injection, the effect of which is generally confined within the peripheral region.

The utilization of hydrogen is gaining increasing attention due to its high heating value and environmentally friendly combustion product. The supercritical water circulating fluidized bed reactor is a promising and potentially clean technology that can generate hydrogen from coal gasification. Cyclone is a vital part of the reactor which can separate incomplete decomposition of pulverized coal particles from mixed working fluid. This paper aims to gain in-depth understanding of the cyclone separation mechanisms under supercritical fluid by computational fluid dynamics (CFD). Although the amount of supercritical carbon dioxide in mixed working fluid is minor, it obviously influences the flow fields and separation efficiency of a cyclone. The simulation results suggest that both the decreasing content of supercritical carbon dioxide and adding the extra dipleg cause the promoting performance of cyclones. Research findings could refine the design of supercritical fluid–solid cyclones.

Iridium (Ir)-based electrocatalysts are widely explored as benchmarks for acidic oxygen evolution reactions (OERs). However, further enhancing their catalytic activity remains challenging due to the difficulty in identifying active species and unfavorable architectures. In this work, we synthesized ultrathin Ir-IrO

Non-uniform sand retention behavior often occurs to the serviced screen deteriorating erosion. However, this phenomenon is poorly understood. This paper presents a numerical study of the sand retention on wire-wrapped screens, with special reference to non-uniform behaviors. This is done by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM). The validity of the model has been validated for dry and wet sand screen systems. It is used here to study sand retention behaviors at different solid concentrations and particle size distributions (PSD). Via this model, five distinct sand retention modes are identified: No sand retention (Mode I), partial sand retention (Mode II), sand retention with slow sequential bridging (Mode III), sand retention with fast sequential bridging (Model IV) and sand retention with instantaneous bridging (Mode V). Modes II and III belong to non-uniform sand retention, which develops strong local flows that induce local erosion or hot spot on the screen. A phase diagram is introduced to predict these five modes and their transition with respect to solid concentration and PSD. Additionally, the predicted flow and force structures are analyzed in detail. The results indicate that the bridging over a slot heavily relies on the particle accumulation on the screen. A new screen with a converging slot configuration is proposed to improve this particle accumulation. This improvement helps develop uniform sand retention on the screen.

This study focuses on the combined effect of particle shape and porosity on the momentum and heat transfer of granular matter under laminar flow. Particle-resolved direct numerical simulations (PR-DNS) are carried out at different working conditions. Numerical results show that both the particle shape (via the aspect ratio, Ar, of the spheroid) and porosity play important roles in affecting the drag coefficient (Cd) and average Nusselt number (Nu). The influence of particle shape on Cd and Nu is regardless of the particle porosity. It is found that the Cd decreases with the increase of Ar for a given Reynolds number (Re). The Nu decreases with the increase of Ar under high Reynolds number (100

The oxy-fuel co-firing of solid fuels (such as coal, biomass, and solid waste) in fluidized beds is one of the most promising technologies for the industrial application of CO2 capture and waste disposal. However, both the practical experimentation and numerical simulations for elucidating co-firing in an oxy-fuel fluidized bed are still limited. In this study, a multiphase particle-in-cell scheme based on a 3D Eulerian–Lagrangian model was further developed following our previous research on oxy-fuel co-firing in a micro fluidized bed (Powder Technol. 2020, 373, 522–534). The refined JL 4-step mechanism for the CO-CO2 homogeneous reactions, the heterogeneous reactions of char oxidation and gasification, the heterogeneous reactions of NO and N2O formation from char-N, and the self-desulfurization effect were comprehensively considered. The improvement of the models was verified through the continuous operation of 10 kWth oxy-fuel fluidized bed tests (Fuel 2021,286,119,312; Energy Fuels, 2020, 34, 7373–7387), and the effects of the biomass blending ratio (Mb) on co-firing characteristics were discussed. It was found that the improvements could enhance the adaptability of the models to the oxy-fuel atmosphere, and the accurate prediction of NO, N2O, SO2. With an increase in Mb, the main reaction zone expanded or moved up along the riser height, and the volume of the high-temperature area increased, which promoted the burnout of particles and CO2 emission when Mb is 50%. The high volatility of biomass increased O2 consumption and CO concentration at the upper part of the riser, reduced N2O formation, and had a significant impact on NO reduction. The low sulfur content and high Ca/S ratio of the biomass considerably reduced the SO2 concentration. The simulation results also provided helpful information for the design and operation control of oxy-fuel co-firing of coal and biomass in a fluidized bed, such as the oxidant supply in different areas and grades, appropriate increase in the riser height, and reasonable adoption of Mb.

Discrete element method is used in this work to examine the mechanisms determining powder deposition efficiency during powder spreading in powder bed fusion additive manufacturing. The results reveal that powder flow in the powder pile is critical for the formation and break of transient jamming. The forces on the underlying part increase first with spreading speed then decrease with a large fluctuation. For varied spreader shapes, a small inclined angle of the spreader surface makes the force barrier farther from the discharging gap, creating a larger region which ensure enough powder supply to the gap. Furthermore, a small inclined angle of the spreader surface close to the gap results in less particle motion conflicts at the gap and ensures larger discharging rate through the gap. This mechanism explains why spreaders with inclined or round surfaces help increase powder deposition efficiency.

In this work, a low-temperature electrostatic precipitator (ESP) experiment platform was established, and two different electrode configurations were compared under various operating parameters to obtain a method for increasing particle capture efficiency. Results show that, in the case of the rated current, the voltage is significantly affected by temperature variations. Concurrently, by appropriately reducing the flue gas flow velocity of the ESP, the charging time of the particles in the ESP flue can be increased, fully charging the particles and improving the collection efficiency. Moreover, experiments revealed that increasing the relative humidity during ESP operation will increase the particle migration velocity and collection efficiency. Finally, when the electrode configurations were changed from a flat collection plate and round electrode to a sharper needle electrode and a concave-convex structure BE plate, resultantly, all efficiencies exceeded 85% under the temperature range from 50 to 150 °C.

Bends are potentially most problematic in a hydraulic conveying pipeline system. This paper presents a numerical study of hydraulic bends, with special reference to the interaction between pipe orientation and flow regime. This is done by the combined approach of computational fluid dynamics and discrete element method facilitated with a wear model. The validity of the model has been verified by comparing the measured and predicted flow properties and erosion depth. On this basis, three pipe orientations: 0° (i.e. horizontal-vertical bend), 45° (i.e. inclined bend), and 90° (i.e. vertical-horizontal bend) are simulated for the conveying speeds of 1.2 m/s, 2.0 m/s and 4.0 m/s. It covers typical flow regimes in a horizontal pipe. Via the simulation outputs, the bend performance is assessed in terms of pressure loss, conveying instability and bend erosion. The results reveal that the pressure drop and erosion rate differ for various pipe orientations and conveying speeds involving different flow regimes. The acceleration/de-acceleration of the particles exiting the bend does not result in a significant additional pressure. The vertical-horizontal bend has low erosion rates benefiting from cluster formation and low pressure, which is not the case at high conveying speeds. By contrast, the inclined bend gives the highest elevation height and does not suffer significant pressure drop, pressure fluctuation, and erosion rate under all the flow regimes considered.

FLDS (Fuel Layered Distribution Sintering) is a technology that can effectively reduce fuel consumption with evenly distributed heat pattern in the sintering bed compared to the conventional iron o...

The minimum fluidization velocity of a supercritical water fluidization bed reactor (SCWFBR) is numerically nvestigated based on coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations. The accuracy of the CFD-DEM model is firstly validated via previously published experimental data. Then, the model is adopted to study the effects of particle size distributions (PSD) on the minimum fluidization velocity in which four types of PSD including Gaussian-type, Mono-type, Flat-type and Binary-type are considered. Numerical results show that the minimum fluidization velocity for the Flat-type PSD is the smallest among the four while the one for the Mono-type PSD is the largest. The minimum fluidization velocities for the Mono-type and Gaussian-type PSD share quite similar values. However, it is conditionally valid when the largest amount of particle size in the Gaussian-type PSD is equal to its mean particle size which is used in the Mono-type PSD. The agreement of the minimum fluidization velocity between Mono-type and Gaussian-type PSD is also influenced by the number of small particles. The mechanism behind these phenomena is revealed by investigating the micro-structure of differently sized particles. Finally, predictive correlations for the minimum fluidization velocity of the SCWFBR are proposed based on the numerical results which demonstrates strong predictive capability for wide PSD.

With increasing social concern towards industrial wastewater treatment, desulfurization wastewater evaporation technology is attracting attention in theoretical investigation and showing competitive capability in practical applications by virtue of its low cost and high efficiency. In engineering practice, the selection of nozzle model, evaporation chamber size and flue gas source need to be carefully determined, ideally with comprehensive understanding of the process mechanism. Important factors to be considered include wastewater evaporation characteristics such as evaporation time, distance, and so on, which are difficult to be obtained directly through physical experiments. Numerical simulation can be utilized conveniently for the extraction of such data and further post analysis. In this study, a salt containing droplet evaporation model is combined with a two-way interphase coupling method to investigate the spray evaporation process. Numerical results show that by increasing the injection velocity and the liquid film thickness, and reducing the flue gas velocity, droplets were observed to be more dispersed in the flue, which in turn enhance the evaporability. The velocity difference between the gas-liquid phases is correlated with the gas-phase turbulent kinetic energy. Non-uniform inlet velocity can increase the flow turbulence intensity. This leads to enhanced droplet evaporation performance on one hand, but increased probability of the droplets hitting the wall on the other hand. From this study, we have also observed that the droplet evaporativity increases with the temperature. Finally, an optimal set of parameters are selected from the simulation exercises to achieve an optimal evaporation outcome. These parameters are introduced in large engineering design to guide the selection of the nozzle model and determine the evaporation chamber size.

This paper aims to establish the relationships between microscopic and macroscopic properties for uniform sphere packings under gravity. The packings are generated by the discrete element method under different conditions with the packing density ranging from about 0.2 to 0.74. The microscopic properties are the structural properties commonly used, including coordination number and various topological and metric properties from the Voronoi-Delaunay tessellation. The results show that these properties can be correlated with packing density. The correlations can be used to estimate different structural properties which are otherwise difficult to obtain in practice.

Particle-fluid flows are commonly encountered in industrial applications. It is of great importance to understand the fundamentals governing the behavior of such a flow system for better process design, control, and optimization. Generally, the particle-fluid flow behavior is strongly influenced by the interaction forces between fluid and particles. Among the various kinds of particle-fluid interaction forces, the drag force is the most essential. This chapter reviews the modeling of drag force for particle-fluid systems: from single particle to multiple particles, monosize to multisize, spherical to nonspherical, and Newtonian fluid to non-Newtonian fluid. Typical drag correlations in the literature are compared and assessed in terms of physical meaning, consistency, and generality.

Packing properties are determined by the dynamic deposition history and affected by many variables. In this work, DEM is used to study the effects of dropping height, deposition intensity and friction coefficient on the dynamic response and stable-state packing properties of ellipsoidal particles. The results demonstrate that with dropping height increasing, packing density increases but the bed becomes less ordered. Dropping height affects the densification process of ellipsoids more significantly than spheres. At high dropping height, the transition period of the orientation angle in the densification process almost disappears for oblate particles, while it becomes longer for prolate particles. With the increase of deposition intensity, packing density decreases significantly, but orientational order changes slightly. With the increase of sliding friction coefficient, packing density and orientational order decrease dramatically. The difference in packing density is mainly caused by dynamic pouring process rather than the densification process.

Powder spreading process is to use a spreader such as blade or roller to spread powder layers for subsequent fusion in powder bed fusion additive manufacturing. In this work, the effects of various spreader geometries on powder spreading are examined by discrete element method (DEM). The results show that a compact region in the powder pile exists. Round and inclined surfaces of blade spreaders allow more particles in the compact region to be deposited compared with vertical blades, thus the powder layer formed is denser. However, they exert larger forces on the underlying part. Inhomogeneity of powder layers is caused by particle burst phenomenon, which is due to particle motion conflict in the compact region rather than large forces. Roller system has largest particle motion conflict thus powder layers formed are sparse and inhomogeneous with small layer gaps. Size segregation in blade systems is not as severe as roller systems.

GPU-based DEM is used to study large-scale particle mixing in bladed mixers. A bladed mixer is scaled-up to three different sizes by maintaining the geometric similarity. Four Froude numbers are selected as the main operating conditions of bladed mixers with different sizes. The results demonstrated that the mixing quality across different mixer sizes is similar at the same Froude number, but it requires a longer mixing time to achieve similar mixing performances as the mixer becomes larger. Correlations to predict the mixing rate, average particle velocity, average total forces, average contact forces and average blade torque as functions of the scale-up ratio and Froude number (or rotation speed) are proposed. A similarity study shows that maintaining the dynamic or kinematic similarity does not produce a similar mixing performance, while maintaining the mixing rate produces a similar mixing performance across all mixers.