Particulate matter (PM) is a well-known air pollutant and most of them are soot emitted from fossil fuel combustion. PM diameter has been decreased with improvement of combustion technology. Especially, the concentration of PM2.5 (diameter less than 2.5 μm) has increased. Fine PM affects serious damage on human body. However, it is difficult for conventional method (e.g., bag filter, diesel particulate filter, and electrostatic precipitator) to remove PM from exhaust gas of combustor. In our research group, fluidized bed is used as a PM removal device. This device collects PM2.5 at high collection efficiency by adhesion force, which is dominant for small particle. On the other hand, the performance of this device strongly depends on fluidization state. Void fraction and gas-solid drag force is large at large flow rate. High void fraction makes PM difficult to approach to bed particle. PM separates from bed particle by large drag force. Thus, it is important for development of this device to understand the mechanism of PM collection.
In this paper, numerical simulation of this device has been performed based on combined computational fluid dynamics (CFD) and discrete element method (DEM) to calculate the trajectory of each individual bed particle and PM. PM is inlet with gas from the bottom side of fluidized bed and transferred upward with gas in fluidized bed while getting adhesion force such as van der Waals force, and separation force such as gas-solid drag force. When PM approaches to bed particle and adhesion force between PM and bed particle becomes larger than separation force, PM adheres to and is held on bed particle. CFD-DEM analysis also shows that adhesion force becomes dominant for PM diameter less than several tens μm at range of superficial velocity 0.3-0.5 m/s.
As the demand of copper has been rapidly increasing, the concentration of copper in raw ores has been decreasing, which has become a major issue for copper production. To meet a strong demand for copper production, it is highly anticipated to develop a new process which can efficiently separate copper minerals from gangue minerals. Among the available comminution techniques, high pressure grinding roll (HPGR) is expected to achieve high mineral liberation with relatively low energy consumption. It is known that HPGR grinding can selectively break grain boundary phases which have mechanical weakness. However, the mechanism of HPGR grinding is still unclear and the effect of HPGR grinding is limited.
The objective of this study was to investigate the effect of HPGR grinding on enhancement of liberation. To achieve this objective, HPGR grinding tests were conducted. The effects of operating conditions such as pressing force, feed amount and an initial roll gap, were investigated. After HPGR grinding, liberation of copper minerals was evaluated by a mineral liberation analyzer (MLA) and image analysis of pictures obtained from MLA was conducted to measure crack size and shape in grinding products. Experimental results indicated that liberation was enhanced because of the increase of cracks by HPGR grinding. These approaches also revealed how many cracks were generated and how the cracks penetrated through an ore or a boundary phase. To support experimental results, a numerical simulation was performed to evaluate forces acting on ores during HPGR grinding. The discrete element method (DEM) coupled with T10 breakage model was applied to reproduce a HPGR grinding. Simulation results suggested that the increase of force acting on ores led to the increase of crack in an ore. Therefore, experimental and simulation results revealed that the increase of the cracks in ores during HPGR grinding enhanced liberation.
Particle de-mixing may occur when particles of different physical properties are mixed. When mixing particles of different sizes, segregation bands and segregation cores may occur in the axial direction and radial direction in a rotating drum, respectively. Although theories and mechanisms of particle segregation have been proposed, a clear understanding of the underlying physics is still lacking. In this talk, size-induced particle segregation phenomena in rotating drums are reported. The mechanism of the segregation structure formation, the three-dimensional segregation patterns observed by experiments and by simulation, the control of the segregation intensity and the application of the segregation patterns will be systematically discussed.
The flow field, temperature distribution and species-in-phase distributions in a 13 MW pulverized-coal boiler are numerically studied using computational fluid dynamics (CFD). The gas phase is modelled using Eulerian frame, and the trajectories of the pulverized coal particles are described by the Lagrangian scheme. As the result, the predicted exhaust temperature and components are well agreed with the experimental data. The regions of the lower oxygen fraction locate approximately at the regions of higher temperatures. The secondary air injection mostly passes to the ceiling of boiler with very short residence time, and the trajectories of coal particles are similar to the secondary air paths. CFD technique successfully predicts the pulverized-coal combustion process in an industrial boiler.
In the past few decades, plastic products from polymers have been extensively used in daily life. In company with the convenience brought by plastic materials, plastic wastes become a critical issue for human society. One practical method to deal with used plastic products is pyrolysis process, which can turn plastic materials into short chain hydrocarbon and solid residues. Carbon black, the major residue material after plastic pyrolysis, has been widely adopted in many industrial applications. However, surface modification treatments are usually required for the recycled carbon black before used in various industrial applications, such as coating or filtration. Among various surface modification techniques, ball milling process has already been proved as a straightforward and easy mechanochemical treatment to modify surface properties of carbon black.
In this study, recycled hydrophobic carbon blacks from waste tire after pyrolysis process are used, and PSS-decorated carbon blacks are prepared through planetary ball milling. The shear force from milling process not only can decorate poly(sodium 4-styrenesulfonate) (PSS) onto carbon black, but also breaks the carbon aggregates into small fragments. The PSS-decorated carbon blacks become hydrophilic, and can be well-suspended in water. Effects of process parameters, such as milling time and solvents, on the surface properties and morphologies of PSS-decorated carbon black will be carefully examined via various analytical techniques, such as FTIR, SEM and thermogravimetric analysis. Dispersion stability tests will also be performed to prove the feasibility of making black pigment ink. Moreover, the printing quality of these inks will be examined to evaluate the possibility of applying recycled materials for printing and painting technology. In summary, this research offers general guidelines for reusing waste materials and pave the way for combining recycled materials with advanced technologies.
