Compare Pilot-Scale And Industry-Scale Models Of Pulverized Coal Combustion In An Ironmaking Blast Furnace

In order to understand the complex phenomena of pulverized coal injection (PCI) process in blast furnace (BF), mathematical models have been developed at different scales: pilot-scale model of coal combustion and industry-scale model (in-furnace model) of coal/coke combustion in a real BF respectively. This paper compares these PCI models in aspects of model developments and model capability. The model development is discussed in terms of model formulation, their new features and geometry/regions considered. The model capability is then discussed in terms of main findings followed by the model evaluation on their advantages and limitations. It is indicated that these PCI models are all able to describe PCI operation qualitatively. The in-furnace model is more reliable for simulating in-furnace phenomena of PCI operation qualitatively and quantitatively. These models are useful for understanding the flow-thermo-chemical behaviors and then optimizing the PCI operation in practice. 2013 AIP Publishing LLC

Contact force models for non-spherical particles with different surface properties : a review

This paper reviews the state-of-the-art contact force models for non-spherical particles, which describe the relationship between the contact force and the geometrical, material, and mechanical properties of the contacting particles. The review aims to select better contact force models to improve the current simplified contact force models used in discrete element method (DEM) simulations. First, the contact force models based on the extension of the classical Hertz theory are reviewed, in which a recent accurate geometrical contact force model is highlighted. Secondly, the research on the effects of different variables such as elastoplasticity, viscoelasticity, adhesion and surface roughness on contact force are reviewed respectively and then incorporated into the accurate geometrical contact force model. Thirdly, tangential force models for non-spherical particles in contact under various loading regimes are reviewed as well. Based on the review, a full set of improved contact force models for DEM is recommended. These contact force models can more accurately predict the contact force and contact area for non-spherical particles, which can be beneficial to the DEM simulation in emerging areas, such as nanoparticles and additive manufacturing

Ab Initio Study of Phase Stability in Doped TiO2

Ab-initio density functional theory (DFT) calculations of the relative stability of anatase and rutile polymorphs of TiO2 were carried using all-electron atomic orbitals methods with local density approximation (LDA). The rutile phase exhibited a moderate margin of stability of ~ 3 meV relative to the anatase phase in pristine material. From computational analysis of the formation energies of Si, Al, Fe and F dopants of various charge states across different Fermi level energies in anatase and in rutile, it was found that the cationic dopants are most stable in Ti substitutional lattice positions while formation energy is minimised for F- doping in interstitial positions. All dopants were found to considerably stabilise anatase relative to the rutile phase, suggesting the anatase to rutile phase transformation is inhibited in such systems with the dopants ranked F>Si>Fe>Al in order of anatase stabilisation strength. Al and Fe dopants were found to act as shallow acceptors with charge compensation achieved through the formation of mobile carriers rather than the formation of anion vacancies

Numerical analysis of effects of specularity coefficient and restitution coefficient on the hydrodynamics of particles in a rotating drum

Various simulations have been conducted to understand the macroscopic behavior of particles in the solid-gas flow in rotating drums in the past. In these studies, the no-slip wall boundary condition and fixed restitution coefficient between particles were usually adopted. The paper presents a numerical study of the gas-solid flow in a rotating drum to understand the effect of the specularity coefficient and restitution coefficient on the hydrodynamic behavior of particles in the segregation process. The volume fraction, granular pressure, granular temperature and their relationships are examined in detail. The boundary conditions of the no-slip and specularity coefficient of 1 are compared. In the simulations, two different sizes of particles with the same density are considered and the Eulerian–Eulerian multiphase model and the kinetic theory of granular flow (KTGF) are used. The results reveal that the hydrodynamical behavior of the particles in the rotating drum is affected by the boundary condition and restitution coefficient. In particular, the increase of specularity coefficient can increase the active region depth, angle repose, granular pressure for both small and large particles and granular temperature for large particles. With increasing restitution coefficient, the angle of repose decreases and granular pressure and temperature increase at the same volume fraction for both small and large particles

A Review of Surface Treatments for Sliding Bearings Used at Different Temperature

The boundary lubrication and dry friction of plain bearings at different work temperature are unable to be avoided under the start and stop condition. The poor lubrication is one reason of bearing broken. In order to improve the tribological properties and select the best treatment for different bearings used at different temperature, the studies of different treatment technologies are reviewed in this paper. The review shows that the shortages of bonding fiber woven materials, inlaying solid lubricating materials, electro plating and magnetron sputtering are poor temperature resistance, low load capacity, environment pollution and low production efficiencies respectively. Based on the analyses and summaries, the liquid dope spraying and thermal powder spraying are suggested to deposit coating on the surface of bearing which working temperature is lower than 200 and above 800°C respectively. However, the technology processes, the mechanisms of spraying and self-lubrication materials should be studied further and deeply

Numerical Analysis of Gas Flow-Slag Surface Interaction in Blast Furnace

An improved understanding of gas flow distribution around the raceway of an ironmaking blast furnace is important for stable operation and improved drainage of molten liquids from the hearth. Previous studies based on 2- and 3-dimensional models with over-simplified raceway phenomena do not provide a quantitative description of liquid-gas interaction. The current paper focuses on the analysis of gas flow near the raceway region and its effect on the liquid surface by using a 3-dimensional sector model. Various BF phenomena and a realistic local coke bed structure, such as the raceway cavity and “birds nest”, are considered. The simulation is conducted using a homogeneous two-phase flow model combined with a model for flow through porous media. The variables considered include the liquid level, location and shape of the cohesive zone and deadman characteristics