Improvement of cyclone separators to reduce air pollution by experiments and simulations

Abstract

This study is based on a comprehensive analysis of the performance of cyclone separators, focusing on the dust collection section. Few studies in the literature have included down-comer tubes at specific higher solid loading conditions and no complete investigation has yet been conducted. However, these studies have provided evidence of greater particle separation by down-comers than by other methods such as additional hoppers and apex cones. Therefore, this study investigated five types of dust collection sections, with and without down-comer tubes. To validate the experimental results, the experiments were also performed under a low velocity condition. Computation fluid dynamics modelling was also performed to evaluate the cyclone flow field and performance with the dust collection sections considered. The evaluation of cyclones with dust collection geometry is important because it has been ignored by many earlier studies even though it is sensible in cyclone operation. For better evaluation, the numerical and experimental results were compared with the theories available in the literature. Although cyclone separators are popular in the particle-handling industry, the enhancement of fine particle collection is still a demanding topic. In industrial applications, filters or recirculation of processed air are usually combined with cyclone operation to increase the efficiency of fine particle separation, which may increase operational costs. Thus this study examined down-comer tubes, which can improve fine particle separation. This study found a remarkable increase in fine particle separation with down-comers, in comparison with conventional hoppers. The increase was pronounced at low solid loading rates. At higher solid concentrations, the increase in the collection efficiency was not obvious and was affected more by the mass loading effect than by its classification. Particle agglomeration was also important in separation at low velocities and high particle concentrations. The numerical results were in agreement with the experiments and discrepancies were due to not considering particle agglomeration and re-entrainment in modelling. The importance of the dust collection section in numerical modelling was also confirmed. The theoretical predictions were not in agreement with the experimental or numerical data due to flaws in the theories, such as a failure to consider particle agglomeration, particle re-entrainment, the anisotropic nature of the particles, the effects of the geometry of the dust collection section and variations in the wall friction with solid deposition. In summary, the findings of this study demonstrate an important method of increasing the fine particle collection of cyclone separators. It also stresses the significance of the dust collection section in the particle separation process both experimentally and numerically. The study further discusses key factors to improve the applicability of the numerical and theoretical methods of cyclone separators to achieve realistic results.

Date of Award	15 Jul 2015
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yee Tak Andrew LEUNG (Supervisor)