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Discrete particle simulation of burden materials in blast furnace top
thesisposted on 23.02.2017, 23:49 by Liu, Sida
The ironmaking process in blast furnace is complicated, and coupled with multiphase flow, chemical reaction and heat transfer, which make it one of the most complicated systems in industry. The process of ironmaking is very difficult to control but only few approaches are available, for example, improve the quality of the raw material, optimize burden distribution, and maximize coal combustion. The burden distribution significantly affects the blast furnace operation efficiency. The void fraction, gas flow distribution and burden descending behaviour depend on the burden distribution. Thus, understanding blast furnace burden distribution is very important for blast furnace operation. In most previous numerical studies, particle shape is not considered. Hence, in the first component, a discrete element method (DEM) based framework is established, aiming to bridge particle shape gap between simulation and practice. Spherical particle surface properties are adjusted by angle of repose to make spheres behave as non-spherical particles in practice. Then experimental results are used to validate DEM in the present study, showing a good agreement. Then variables related to burden distribution are investigated, such as particle surface properties, chute angles and discharge rate. Chute wear prediction has always been a problem for blast furnace schedule maintenance. In the second part, chute flow is analyzed in great details, and the microscopic information is generated to get better understanding of chute flow and thus used to predict the wear issue for rotating chute. Then size segregation phenomenon is also studied for both chute flow and in burden profiles. And finally, a practice case is simulated to further prove the capability of present DEM model, indicating DEM is capable to use for practice application. The purpose of taking control of burden distribution is taking control of the gas distribution in blast furnace thus can obtain smooth operation. In the third part, practice cases are simulated and analyzed. A thin sector frame is introduced to reduce total particle number in the system thus multi-layer burden profiles are studied, showing burden profile keeping changing in the charging process. Gas flow is simulated by coupling DEM with Computational Fluid Dynamics (CFD) and its distribution for different burden profiles are analyzed qualitatively. Hopper is the essential feeding mechanic for blast furnace, thus fundamental study is required in this area. In the fourth part, ellipsoidal particles are simulated in a rectangular hopper to study hopper flow phenomenon. The focus is particle shape effect on wall stress, meanwhile flow patterns and discharge rate have also been studied. The results indicate that particle shape changes the internal properties thus bulk material properties hence make impact on wall stress. The particles discharged from hopper can naturally form a pile, and the particle shape effect on angle of repose and force distributions are investigated. Furthermore, varies factors’ effects on stress dip phenomenon have been investigated.