Prediction of burden distribution and electrical resistance in submerged arc furnaces using DEM modelling
Date
2024-03
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Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: This thesis investigates material segregation and its effect on electrical properties in the burden layer of a submerged arc furnace (SAF) used to produce ferrochrome. The study shows some correlation between material segregation and electrical resistance, which affects the efficiency of chemical reactions and energy efficiencies. Efficient control of raw material distribution ensures consistent heating and chemical conversion, maximising the quality and quantity of ferrochrome produced. Controlling electrical resistance is therefore important for optimising power utilisation. Variations in burden layer segregation can result in electrical inefficiencies, affecting energy consumption and manufacturing costs. A discrete element method (DEM) model developed using the LIGGGHTS-PUBLICĀ® software was applied to study material flow and distribution in the furnace burden, focussing on mechanical interactions influenced by intrinsic properties, interaction parameters, and morphological parameters. A resistance calculation algorithm is used to post-process the DEM results and assess electrical conduction conditions, including electrode-bath and electrode-electrode interactions using the DC circuit approximation method. The study uses cold-flow experimental testing and DEM simulations to characterise and calibrate material properties. Pellets are treated as approximately spherical, while anthracite and quartz particles are more irregular. Photogrammetric studies were conducted on the reductant and flux particles, and a multisphere approach was used to represent their shape characteristics in the DEM models. A base case furnace model was developed using material parameters from literature and experiments, and flow behaviour in the furnace burden was simulated using LIGGGHTS-PUBLICĀ® to calibrate specific properties such as the coefficient of friction between materials and the rolling friction of pellets. The base case model was then used for sensitivity studies in three key domains: morphological parameters (particle size and shape), intrinsic material properties (density, Poisson's ratio and Young's modulus), and parameters of interaction (restitution and friction coefficients). The model and related sensitivity cases were run using a high-performance computing cluster at the Centre for High Performance Computing in Cape Town, South Africa. The study demonstrates the potential value of DEM in studying material flow dynamics and resistance phenomena in SAFs used for the smelting of ferrochrome ore. The models show distinct particle segregation patterns, especially among anthracite and quartz, alongside walls and in the central delta region. The study suggests that morphological parameters such as particle shape, reductant fractions, reductant density, and particle size had an effect on both the particle segregation and resistance of the burden. The mechanical interaction parameters, such as the coefficient of friction and the coefficient of restitution, did not appear to show any significant correlations. In the current study the furnace geometry did not appear to show any significant effect on the resistance. Electrode length changes were examined and had a strong influence on resistance, although the segregation behaviour remained largely unchanged. Understanding the relationship between material segregation and electrical resistance is potentially an important factor for reliable and economical ferrochrome production methods. The introduction of DEM modelling provides an opportunity to gain a deeper understanding of material movement and electrical interactions within the furnace burden layer, and this insight may help with adapting to changes in the available raw materials and enhancing furnace productivity and efficiency.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MEng)--Stellenbosch University, 2024.
Keywords
Submerged arc furnace; Ferrochrome; DEM; Resistance; Segregation