Study On The Separation Characteristic Of A Cyclone Separator With Different Dust Outlet Geometries And Operating Conditions

Cyclone separators have been one of the oldest and most popularly used industrial particulate control devices for the removal of dispersed particles from their carrying fluids because of their simplicity, easiness and low costs in terms of construction, operation, maintenance and energy consumption. With the use of suitable materials and methods of construction, cyclone separators can be operated under extreme operating conditions, especially at temperatures over 900℃, conditions that almost exclude the application of other separation technologies. Some of the best examples are cyclone separators employed in PFBC (Pressurized Fluidized Bed Combustion), IGCC (Integrated Gasification and Combined Cycle) and FCC (Fluidized Catalytic Cracking) processes. In these harsh environments, cyclone separators are nowadays the sole, fully commercial solution to the removal of particles from elevated-temperature gases. Their main disadvantage, however, is low efficiency for particles less than 5 microns in size.In order to increase the separation efficiencies, improve the geometries and optimize the sizes of cyclone separators, the rule of turbulent flow field and the gas-solid separation characteristic should be studied in detail. Experimental studies and numerical simulations are used to analyze the strongly turbulent flow field and the gas-solid separation characteristic in this thesis. Experimental studies of flow field are conducted by Particle Image Velocimetry (PIV), and the gas flow fields of the vertical tube and dustbin in cyclone separators with different dust outlet geometries and separation performances of different cyclone separators are measured. Under the RSTM in Fluent code, although the first-order upwind scheme discretization can yield better convergence, it generally will lead to less accurate results. Therefore, the QUICK discretization scheme is used in calculating momentum, turbulence kinetic energy, its dissipation rate equations and Reynolds stress equations. Numerical studies are conducted for different inlet particle concentrations of a cyclone separator. One-way coupling, two-way coupling of dispersed particle model (DPM) and simplified Eulerian model-Algebraic Slip Mixture Model (ASMM) are used. Aiming at very limited experimental data of the cyclone separator working at different temperature, pressure and inlet particle concentration, the separation performances of these operating conditions are predicted by means of computational fluid dynamics (CFD) technology, and the separation performances at the representative temperature, pressure and inlet particle concentration of PFBC, IGCC and CFBC are predicted. The predicted separation performances are compared with the presented empirical models and experimental data. The results show: (1) The predicted separation efficiencies are in more agreement with the experimental data comparing to the empirical and semi-empirical model. The results also show that it is feasible and cheap to investigate the separation performance of the cyclone separator by means of CFD technology.(2) The prolonged cyclone separator can make the vortex end locate in the vertical tube and even in the dustbin, and increase the efficient separation space, thus improve its separation performance. However, for an even longer tube, the separation efficiency is slightly reduced. Therefore, there is an optimal tube length for a given cyclone. On the other hand, the cyclone separator with bottom air extraction can increase the separation efficiency, but there is an optimal air extraction rate, which is the same as the length of the vertical tube. When the air extraction rate is in excess of this optimal value, the separation efficiency increases slightly. For the cyclone separator that is presented in this paper, the optimal vertical tube length...