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 Impacts of Three Flamelet Burning Regimes in Nonlinear Combustion Dynamics

Axisymmetric simulations of a liquid rocket engine are performed using a delayed detached-eddy-simulation (DDES) turbulence model with the Compressible Flamelet Progress Variable (CFPV) combustion model. Three different pressure instability domains are simulated: completely unstable, semi-stable, and fully stable. The different instability domains are found by varying the combustion chamber and oxidizer post length. Laminar flamelet solutions with a detailed chemical mechanism are examined. The $\beta$ Probability Density Function (PDF) for the mixture fraction and Dirac $\delta$ PDF for both the pressure and the progress variable are used. A coupling mechanism between the Heat Release Rate (HRR) and the pressure in an unstable cycle is demonstrated. Local extinction and reignition is investigated for all the instability domains using the full S-curve approach. A monotonic decrease in the amount of local extinctions and reignitions occurs when pressure oscillation amplitude becomes smaller. The flame index is used to distinguish between the premixed and non-premixed burning mode in different stability domains. An additional simulation of the unstable pressure oscillation case using only the stable flamelet burning branch of the S-curve is performed. Better agreement with experiments in terms of pressure oscillation amplitude is found when the full S-curve is used.Comment: 25 pages, 12 figures. Submitted to Combustion and Flame for a Special Issu

Visualization and modeling of evaporation from pore networks by representative 2D micromodels

Evaporation is a key process for the water exchange between soil and atmosphere, it is controlled by the internal water fluxes and surface vapor fluxes. The focus of this thesis is to visualize and quantify the multiphase flow processes during evaporation from porous media. The retained liquid films in surface roughness (thick-film flow) and angular corners (corner flow) have been found to facilitate and dominate evaporation. Using the representative 2D micromodels (artificial pore networks) with different surface roughness and pore structures, this thesis gives visualizations of the corner and thick-film flow during the evaporation process, presents the enhanced hydraulic continuity by corner and thick-film flow, and tests the validity of the SSC-model which assumes corner flow is dominant for the mass transport during evaporation. Surface roughness and wettability are proved both experimentally and theoretically to play a key role for the time and temperature behaviors of the evaporation process, besides, this thesis shows that for a consistent description of the time-dependent mass loss and the geometry of the corner/thick-film flow region, the fractality of the evaporation front must be taken into account

Nerva-derived reactor coolant channel model for Mars mission applications

NERVA-Derived Reactor Coolant Channel Model for Mars Mission Applications presents the results of a computational fluid dynamics (CFD) study of a 1.3m NERVA-Derived Reactor (NDR) coolant channel; The CFD code FLOW-3D was used to model the flow of gaseous hydrogen through the core of a NDR. Hydrogen passes through the core by way of coolant channels, acting as the coolant for the reactor as well as the propellant for the rocket. Hydrogen enters the channel in a high density/low temperature state and exits in a low density/high temperature state necessitating the use of a compressible model. Design specifications from a technical paper were used for the model; It was determined that the pressure drop across the length of the channel was higher than previously estimated (0.9 MPa), indicating the possible need for more powerful coolant pumps and a re-evaluation of the design specifications

Modeling single-phase flow and solute transport across scales

textFlow and transport phenomena in the subsurface often span a wide range of length (nanometers to kilometers) and time (nanoseconds to years) scales, and frequently arise in applications of CO₂ sequestration, pollutant transport, and near-well acid stimulation. Reliable field-scale predictions depend on our predictive capacity at each individual scale as well as our ability to accurately propagate information across scales. Pore-scale modeling (coupled with experiments) has assumed an important role in improving our fundamental understanding at the small scale, and is frequently used to inform/guide modeling efforts at larger scales. Among the various methods, there often exists a trade-off between computational efficiency/simplicity and accuracy. While high-resolution methods are very accurate, they are computationally limited to relatively small domains. Since macroscopic properties of a porous medium are statistically representative only when sample sizes are sufficiently large, simple and efficient pore-scale methods are more attractive. In this work, two Eulerian pore-network models for simulating single-phase flow and solute transport are developed. The models focus on capturing two key pore-level mechanisms: a) partial mixing within pores (large void volumes), and b) shear dispersion within throats (narrow constrictions connecting the pores), which are shown to have a substantial impact on transverse and longitudinal dispersion coefficients at the macro scale. The models are verified with high-resolution pore-scale methods and validated against micromodel experiments as well as experimental data from the literature. Studies regarding the significance of different pore-level mixing assumptions (perfect mixing vs. partial mixing) in disordered media, as well as the predictive capacity of network modeling as a whole for ordered media are conducted. A mortar domain decomposition framework is additionally developed, under which efficient and accurate simulations on even larger and highly heterogeneous pore-scale domains are feasible. The mortar methods are verified and parallel scalability is demonstrated. It is shown that they can be used as “hybrid” methods for coupling localized pore-scale inclusions to a surrounding continuum (when insufficient scale separation exists). The framework further permits multi-model simulations within the same computational domain. An application of the methods studying “emergent” behavior during calcite precipitation in the context of geologic CO₂ sequestration is provided.Petroleum and Geosystems Engineerin

Thirteenth Workshop for Computational Fluid Dynamic Applications in Rocket Propulsion and Launch Vehicle Technology

This conference publication includes various abstracts and presentations given at the 13th Workshop for Computational Fluid Dynamic Applications in Rocket Propulsion and Launch Vehicle Technology held at the George C. Marshall Space Flight Center April 25-27 1995. The purpose of the workshop was to discuss experimental and computational fluid dynamic activities in rocket propulsion and launch vehicles. The workshop was an open meeting for government, industry, and academia. A broad number of topics were discussed including computational fluid dynamic methodology, liquid and solid rocket propulsion, turbomachinery, combustion, heat transfer, and grid generation

Process Modeling in Pyrometallurgical Engineering

The Special Issue presents almost 40 papers on recent research in modeling of pyrometallurgical systems, including physical models, first-principles models, detailed CFD and DEM models as well as statistical models or models based on machine learning. The models cover the whole production chain from raw materials processing through the reduction and conversion unit processes to ladle treatment, casting, and rolling. The papers illustrate how models can be used for shedding light on complex and inaccessible processes characterized by high temperatures and hostile environment, in order to improve process performance, product quality, or yield and to reduce the requirements of virgin raw materials and to suppress harmful emissions

Tracing back the source of contamination

From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer

The influence of physico-chemical surface properties and morphological and topological pore space properties on trapping (CCS) and recovery efficiency (EOR): a micromodel visualization study

We theoretically and experimentally investigate the impact of pore space structure, wettability, and surface roughness on the displacement front, trapping, and sweeping efficiency at low capillary numbers. The microstructure of (i) 2D geologically-realistic media (2D natural sand and sandstone), (ii) a topological 3D-2D-transformation (2D sand analog), and (iii) geometrically representative media (Delaunay Triangulation) were studied over a wide range of wettability from water-wet to oil-wet systems provided by using various fluid-pairs. We observed the transition (compact to fractal) in the displacement front caused by local instabilities identified by Cieplak and Robbins. The trapping efficiency of 2D natural microstructures showed a non-monotonous dependency on wettability, whereas a crossover from no trapping to maximal trapping was observed in 2D patterns of circular grains. For the first time, we compared identical experimental microstructures with simulation, capturing the key elements of the invasion process. We demonstrated that corner flows occur particularly in low-porosity media, where the smaller grain-grain distance hindered the corner-flow bridging. These insights could improve the CO2 geological storage and Enhanced Oil Recovery processes