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Title: A holistic research approach for the investigation of air current segregation in alumina silos
Author: Zigan, Stefan
ISNI:       0000 0001 3577 926X
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 2008
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Although the production of aluminium is a well- established process, quality fluctuations frequently occur because of its main feedstock, alumina. One of the reasons for the problems is the segregation of particles during the storage of alumina in silos. Air current segregation (ACS) was identified as one mechanism causing segregation. During the filling of a storage silo with alumina powder, air is simultaneously entrained. As a result, airflow circulation arises and separates fine particles from th.e bulk stream, which are then deposited to the outer areas of the silo. The literature claims that factors such as powder feeding height and rate, and air extraction heavily influence the occurrence of this phenomenon in the silo. However, in the literature, no quantitative experimental data are presented. Due to the lack of a detailed physical understanding of ACS, it was the objective of this research to investigate the relationship between different parameters, e.g. the powder feeding rate and air extraction rate, and ACS. A further objective of this research was to find a scaling method that could be used to scale results between different sized experiments. First, all significant parameters were identified by experiments and dimensional analysis was applied to develop a scaling rule. Five dimensionless groups were obtained, which was unwieldy. To reduce the number of dimensionless groups, physical properties were lumped into the terminal velocity. This simplified approach gave three dimensionless groups. These were tested in an air silo and a cylindrical silo filled with water. The results showed that the dynamics of the particle-air flows in the water and air silo were slightly different. Further, experiments included the visualisation of the particle jet in an industrial storage unit, a two dimensional rack, and in laboratory cylindrical silos. To measure the particle velocities in a laboratory cylindrical silo, Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) were used and results showed that a dense particle jet leads to minute segregation. In addition, process parameters, e.g. the powder feeding rate and air extraction rate, were varied in cylindrical silos and the extent of ACS measured.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available