Numerical Simulation Of Dense Gas-solid Separation In Cyclone Separators

Multiphase flow is a fundamental physical phenomenon prevalent in nature and industrial processes, and has very wide range of application, such as dust air, debris flows, sandstorms flow, powder pneumatic conveying, separation and collection of coal combustion and conversion, other applications where multiphase flow problem occur include the fluidized bed reactor in the coal combustion, petroleum processing industry spray combustion, solid propellant rocket nozzle flow and materials industry.In industrial applications, we often encounter the phenomenon of separation of multiphase flow. Many industrial processes, such as coal and waste materials combustion, mineral processing, food processing, soil remediation, waste treatment, oil refining, apply the phenomenon of particle separation.Several technologies, including fabric filters, dust collectors and cyclone separators can be used for gas-solid separation. Some separators are not suitable for many industrial applications, but Cyclones play a critical role in separation of solid particles in a flowing fluid. Cyclones Separators are widely used in many industrial sectors such as in the petrochemical and process industries to separate dust from gas steams or for product recovery.In the last decade, Cyclones separators have been the subject of several experimental and numerical researches to improve and this involves trying to treat several parameters involved in modifying the behavior of their efficacy. However, due to factors, that affect the performance of cyclones and the gas-solid two-phase flow is extremely complex and then involves many of the basic disciplines of fluid mechanics, thermodynamics, heat and mass transfer, combustion and rheology.With the development of computer technology and computational method, numerical simulation has become one of the most promising methods for studying gas-solid flows. Continuous improving of the numerical simulation methods has important significance to further study of the complex mechanism and effect factors of gas-solid flows. The present contribution aims to add more to the existing knowledge on the functioning of cyclones which represents one of the most recent applications of the technique of separation by centrifugal force. The main objective of the present research is to study the behavior of dense gas solid separator within different type of cyclones. The research aims to provide a better understanding of the effect of cyclone geometry. Two turbulence model and Eulerian-Eulerian approach will be combined to study and describe the dense fluid flow and the performance of cyclone. The effect of cyclone geometry, the effect of turbulence model and the effect of solid concentration on the cyclone separators are investigate.The scope covered in the present research is outlined in the following paragraphs:(1) Firstly, the numerical simulation of gas and solid flow were performed using conventional cyclone separator with four types of inlet configuration. In this section, we used Renormalization group k-epsilon (RNG k-ε) and Reynolds stress model (RSM) model in Fluent to study numerical simulation of gas and particle flow in cyclone separator. The turbulent model is verified by comparing the RNG k-ε and RSM results in term of gas pressure field, gas and solid volume fraction. The effects of turbulent model, solid inlet volume fraction and inlet geometry are investigated based on the velocity components, pressure drop and cyclone efficiency.(2) In the second part simulations are relative to the square cyclone separator, the flow behavior of gas and particles within a square cyclone separator is simulated by means of computational fluid dynamics. The RNG k-ε model and the RSM were used to model gas turbulence, and Eulerian approach to model gas-solid two phase flow. The flow behavior is examined in terms of tangential velocity components, static pressure and pressure drop contour plots for flow field and solid volume fraction. The effects of the turbulence model and solid volume fraction on the square cyclone are discussed. The results indicate that the pressure drop increases with increasing solid volume fraction, and increase with increasing inlet velocities for two turbulence models, moreover, simulations were compared with pressure field. For all runs, the RSM model gives a higher pressure drop compared to the RNG k-ε model. The RSM model provides well the forced vortex and free vortex, and captures better the phenomena occurring during intense vortex flow in the presence of walls within cyclone separators. The results showed that square cyclone with different inlet geometries would increase the pressure drop and decrease the separation efficiency as function of inlet angle. Note that the effects of the cyclone inlet configuration angle on pressure drop and collection efficiency are opposite. Increasing the inlet width will save more driving power but leads to reduced collection efficiency.(3) Finally, The RNG k-ε and RSM and Eulerian approach will be combined to study and describe the dense fluid flow and the performance of cyclone in horizontal cyclone separator. The effect of two turbulence model and solid inlet volume fraction based on the distributions of the flows fields, and cyclone performance were studied and the results illustrated that by increasing of solid volume fraction the pressure drop in horizontal cyclone increases but the collection efficiency decreases.