Discrete Simulation of Gas-solid Flow and Softening-melting Behaviour in a Blast Furnace

The blast furnace is a complicated multiphase flow reactor with hazardous working conditions, and its understanding is still a challenge in research community. In the recent decades, the discrete element modelling is becoming a popular tool to study this process, especially for the particle related phenomena, such as gas-solid flow, particle softening-melting behaviour and gas-solid heat transfer. This work aims to develop some new and better methods to describe this process based on the discrete model. The discrete model shows some unique advantages in describing particle motion; however the high computing cost limits its application in the study of blast furnace. A sector model is successfully developed to represent the full 3D cylinder vessel, which can effectively reduce the number of particles and hence the computational cost. Its validity is first examined through two common industrial processes; hopper flow and pile formation. The results generated by the sector model are exactly the same as the full 3D model, but saved 90% computing time. Then, the sector model is applied to study the gas-solid flow in a blast furnace, and the comparison between the sector model and the slot model are given in detail. Understanding the particle softening and melting behavior in the cohesive zone is the basis to describe the gas/liquid distribution and thermal-chemical behavior in this zone, which is critical to understanding the complex physical and chemical phenomena in a blast furnace. The CFD-DEM method accompanying with the gas-particle heat transfer is one powerful tool to carry out this study. The softening and melting behaviour of wax particles is successfully captured, by implementing the correlation between Young’s modulus and temperature of wax. And the multi-layer behaviour is also studied and then a parametric study. Further, in order to study the heat transfer in the raceway of blast furnace, the gas-solid heat transfer based on the discrete model is first used in a moving bed. The simulation is quantitatively consistent with the previous experimental data, that demonstrating the capability to accurately describe the thermal phenomenon in the raceway

The XDEM Multi-physics and Multi-scale Simulation Technology: Review on DEM-CFD Coupling, Methodology and Engineering Applications

The XDEM multi-physics and multi-scale simulation platform roots in the Ex- tended Discrete Element Method (XDEM) and is being developed at the In- stitute of Computational Engineering at the University of Luxembourg. The platform is an advanced multi- physics simulation technology that combines flexibility and versatility to establish the next generation of multi-physics and multi-scale simulation tools. For this purpose the simulation framework relies on coupling various predictive tools based on both an Eulerian and Lagrangian approach. Eulerian approaches represent the wide field of continuum models while the Lagrange approach is perfectly suited to characterise discrete phases. Thus, continuum models include classical simulation tools such as Computa- tional Fluid Dynamics (CFD) or Finite Element Analysis (FEA) while an ex- tended configuration of the classical Discrete Element Method (DEM) addresses the discrete e.g. particulate phase. Apart from predicting the trajectories of individual particles, XDEM extends the application to estimating the thermo- dynamic state of each particle by advanced and optimised algorithms. The thermodynamic state may include temperature and species distributions due to chemical reaction and external heat sources. Hence, coupling these extended features with either CFD or FEA opens up a wide range of applications as diverse as pharmaceutical industry e.g. drug production, agriculture food and processing industry, mining, construction and agricultural machinery, metals manufacturing, energy production and systems biology

The eXtended Discrete Element Method (XDEM): An Advanced Approach to Model Blast Furnace

The blast furnace iron making is the oldest but still the main method to produce liquid iron through sequential reduction processes of iron ore materials. Despite the existence of several discrete and continuous numerical models, there is no global method to provide detailed information about the processes inside the furnaces. The extended discrete element method known as XDEM is an advance numerical tool based on Eulerian–Lagrangian framework which is able to cover more information about the blast furnace process. Within this platform, the continuous phases such as gas and liquid phases are coupled to the discrete entities such as coke and iron ore particles through mass, momentum and energy exchange. This method has been applied to the shaft, cohesive zone, dripping zone and hearth of the blast furnace. In this chapter, the mathematical and numerical methods implemented in the XDEM method are described, and the results are discussed

Experimental and Numerical Studies of Burden Layers at Blast Furnace Charging

The blast furnace (BF) is the main production unit in the processing of iron ore to molten iron (“hot metal”) in the steelmaking industry. It is a large process with huge throughput and energy consumption, so even a slight improvement of its efficiency can lead to considerable reductions in costs and harmful emissions. The charging system is the only way by which the initial distribution of the raw materials can be controlled. This distribution not only determines the structure of the arising burden bed, but also the chemical and thermal efficiency of the gas. These are crucial factors for achieving a low rate of reductants, a long life length and a more sustainable operation of the furnace. Focusing on the behavior of particles forming heaps and layers in granular systems, this thesis has studied some questions related to burden-layer formation, burden bed properties, burden descent and gas flow distribution in the blast furnace throat and shaft. Firstly, the effects of particle shape and physical parameters on the porosity and angle of repose of iron ore particle heaps were simulated by discrete element method (DEM). Models of non-spherical particles (cylinders and cones) were established using the sphere-cluster method. For comparison and model validation, small-scale experiments were undertaken with particles of the same shapes prepared in the laboratory. The consistency of the simulated and experimental results demonstrate that the established DEM model can be used for the prediction of the porosity of a particle system. Some key physical parameters of the main burden materials (pellets, sinter and coke) were measured and validated by experiments. The experimentally determined parameters were the Young’s modulus, Shear modulus, Poisson’s ratio, particle density, coefficient of restitution, as well as coefficients of static and rolling friction. The experimental and calculated results were found to exhibit good agreement, which confirmed that the measured DEM parameters were of sufficient accuracy to be used in simulation of the burden distribution and descent in the blast furnace. DEM models describing the porosity distribution and radial ore-to-coke mass ratio of the burden layers in the blast furnace shaft were successfully established based on a bell-less burden charging system with 2D slot and 3D sector throat models. An experimental bell-less charging system with a scale of 1:10 compared to an industrial BF was designed and operated in a set of experiments. DEM simulations of the corresponding system showed results in general agreement with the empirical findings, validating the numerical models. Two kinds of non-uniform descent of burden in the upper part of the blast furnace were considered in a numerical DEM-based model, where the descent rate in the furnace center is greater than the descent rate at the wall or vice versa. The results showed that the ore-to-coke ratio decreases where the burden descent rate is low and increases where the descent rate is high. Finally, the effect of intermittent charging on the thermal and flow conditions in the upper shaft was analyzed by Computational Fluid Dynamics (CFD) combined with DEM. A model of the counter-current flow of gas and solids and the temperature of the two phases in a simplified setup was developed. The results clarified how the temperature and velocity of the ascending gas are affected by the intermittent charging.Masugnen är den huvudsakliga processenheten vid produktion av råjärn för stålframställning. Den är en industriell reaktor med mycket stor genomströmning av material. Ugnen har en hög energiförbrukning, vilket innebär att redan små relativa förbättringar i driften kan har stora implikationer för material- och energiåtgång samt för de utsläpp som förorsakas av processen. Masugnens chargering, d.v.s. inmatningen av det fasta råmaterialet vid toppen, är av stor betydelse för styrningen av råmaterialets radiella fördelning i ugnens övre del. Chargeringen bestämmer beskickningens struktur imasugnsschaktet, vilket påverkar ugnens termiska och kemiska verkningsgrad. Dessa faktorer är centrala för att uppnå driftpunkter med låg förbrukning av reduktionsmedel, lång ugnskampanj samt en hållbar järnframställning. Föreliggande avhandling studerar beteendet hos partiklar som bildar högar och lager i granulära system. Avhandlingen behandlar frågor av speciell relevans för bäddens egenskaper i masugnsschaktet, där lager av olika beskickningsmaterial bildas vid chargeringen och efter det långsamt sjunker nedåt i ugnen. För att beskriva hur gasen fördelas i schaktet måste även porositeten hos materialbädden vara känd. I den första delen av arbetet studerades inverkan av partikelform och fysikaliska parametrar på porositeten och rasvinkeln för högar av järnbärare. Systemet simulerades med diskreta element-metoden (DEM), där partiklar med annan form är sfärisk skapades genom att klumpa ihop överlappande sfärer (eng. sphere-cluster). För jämförelse och för validering av den matematiska modellen utfördes småskaliga laboratorie-experiment med partiklar av samma typ. Överensstämmelsen mellan de simulerade och experimentella resultaten visade att DEM-modellen kan användas för att prediktera porositeten hos partikelsystemet. Några viktiga fysikaliska parametrar hos de huvudsakliga beskickningsmaterialen (pelletar, sinter och koks) uppmättes och validerades med hjälp av experiment. De parametrar som bestämdes experimentellt var elasticitetsmodulen, skjuvmodulen Poissons konstant, partikeldensitet, restitutionskoefficienter, samt statiska och rullnings-friktionskoefficienter. De experimentella och simulerade resultaten befanns överensstämma väl, vilket bekräftade att DEM-parametrarna som bestämts var tillräckligt noggranna för att kunna utnyttjas vid simulering av beskickningsfördelning och -sjunkning i masugnen. DEM-modeller som beskriver bäddporositetens och den radiella malm-koksfördelningen hos beskickningen i masugnsschaktet skapades för ett system med s.k. Paul Wurth-chargeringsmål med två- eller tredimensionella modeller för masugnens gikt. Ett experimentellt klocklöst (eng. bell-less) uppsättningsmål i laboratorieskala i 1:10-skala jämfört med en industriell ugn byggdes och utnyttjades i experiment. DEM-simuleringar av motsvarande system gav resultat som generellt överensstämde med de experimentella resultaten, vilketvaliderade de matematiska modellerna. Två typer av ojämn sjunkning av beskickningen i schaktet studerades även numeriskt med hjälp av en DEM-modell, där bädden simulerades sjunka snabbare eller långsammare i masugnens centrala del. Resultaten visade att malm/koks-förhållandet avtar i regioner där bädden sjunker långsamt, medan kvoten ökar i regioner där sjunkhastigheten är hög. I arbetets sista del studerades hur en satsvis chargering påverkar det termiska och flödesmässiga dynamiska tillståndet hos den översta delen av masugnsschaktet med hjälp av flödessimulering (eng. Computational Fluid Dynamics, CFD) kombinerad med DEM, s.k. CFD-DEM-teknik. En förenklad och nerskalad modell utvecklades, som beskriver motströmsflödet av gas och beskickningsmaterial och temperaturerna hos de två faserna. Modellen klargjorde hur temperaturerna och gashastigheten påverkades av den oregelbundna chargeringen, vilket förklarar fenomen som man kan observera vid ugnstoppen i den verkliga driften av masugn

The Study of the Distribution and Deformation of Burden Layer in 250 Ton/Day Mini Blast Furnace Using Discrete Element Method

Based on the abundant nickel ore resources in Indonesia, it is necessary to develop nickel ore processing technology. One of the commercially proven nickel processing technology is Mini Blast Furnace (MBF). The feeding process in MBF using charging system. So, the burden material distribution in MBF can be controlled. The burden material controlling is important process in MBF. The distribution of burden material will affect the gas flow in MBF. This research focuses to study the effect of large bell diameter size to burden materials distribution in MBF using Discrete Element Method. After analysis, the differences of large bell diameter size will affect the burden materials distribution. If the diameter of large bell is greater, the impact point during charging process will be closer to the wall area. Then, the impact area on the surface of the layer will be on top of the layer. The distribution of burden materials in MBF is influenced by large bell size, kinetic energy at impact, particle mass, and particle size and layer stability. For particles distribution, the particles with small density (coal and dolomite) tend to be concentrated in the center zone. On the other hand, the particles with large density (ore) tend to be concentrated in the intermediate and peripheral zone. For the MBF start-up process, the best gas flow can be achieved by using large bell and MBF inner diameter ratio of 7: 10