Analysis of factors affecting the separation efficiency of cyclone separators
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Abstract: Numerical simulations using ANSYS-FLUENT were conducted to analyze the pressure distribution and flow field velocity distribution within a cyclone separator, and to examine the influence of different gas velocities and cylinder diameters on the separation efficiency of the cyclone separator. The results show that the separation efficiency of the cyclone separator increases with increasing gas velocity within a certain range, but it decreases after reaching a certain value ； For a new type of cyclone barrel structure, reducing its cylinder diameter from 5.8 m to 5.0 m improved the separation efficiency of the cyclone separator. Keywords: cyclone, separation efficiency, numerical analysis. 0 Introduction The main function of a cyclone separator is gas-solid separation. Thanks to its simple structure, ease of operation and maintenance, stable performance, and the ability to operate for long periods under harsh conditions such as high temperature and high pressure, it is widely used in industries such as cement, petroleum, and metallurgy. However, due to the complex highly rotational turbulent flow inside the cyclone separator, as well as the instability inherent in the rotational motion of the airflow, the actual separation process in the cyclone separator is very complex. In actual operation, it can be observed that backmixing and entrainment occur in the cyclone separator; that is, the flue gas carries some of the material out through the exhaust port, which affects the separation efficiency of the cyclone separator and increases energy consumption. Research has shown that this phenomenon occurs due to secondary flows within the cyclone separator, which result in phenomena such as a dust ring at the top and short-circuit flows inside the cyclone separator. As a consequence, the cyclone separator’s efficiency in separating fine particles is reduced, leading to a lower overall separation rate. To address issues related to the separation efficiency of cyclone separators, the distribution of the internal flow field, and gas-solid heat transfer, many scholars at home and abroad have employed numerical methods for research. Wangugu Jun and others studied the effect of temperature on the particle concentration distribution within the cyclone separator, as well as the effect of pressure on the flow field inside the separator. Liang Shaoqing and others used the RSM model to analyze the characteristics of the velocity distribution inside the cyclone separator. Zhou et al. studied the separation of ultra-light particles in a cyclone separator. Sela-mi et al. studied the causes of pressure drop in cyclone separators and proposed suggestions on how to reduce the pressure drop within them. Ma et al. used the RNG turbulence model to numerically simulate the motion of particles inside a small cyclone. Wang et al. used the Reynolds stress model to investigate the effects of particle size and gas velocity on the separation efficiency of cyclone separators. Bogodage et al. studied the effect of the feed port on the separation performance of cyclones. FLUENT is a widely used CFD software package in the international community, capable of solving engineering problems related to fluids and chemical reactions accurately and efficiently. It is extensively applied in fields such as aerospace and turbomachinery. This paper uses ANASY-FLUENT to investigate the factors affecting the separation efficiency of cyclone separators, and also studies the separation efficiency of a cyclone separator with a new structure.
Calculation methods and boundary conditions: The software used for the simulation analysis in this paper is Fuen. In this software, a pressure solver was selected for transient calculations, and the gravitational acceleration in the Z direction was taken into account. The SIMPLE algorithm was used as the coupling algorithm for pressure and velocity. For the turbulence model selection, the RNG version of the k-epsilon model was chosen. RNG takes turbulent vortices into account; other parameters have been modified compared to the standard k-e model, which improves accuracy and makes it suitable for this simulation. The motion of fluids is governed by fundamental governing equations, including the mass conservation equation, the momentum conservation equation, and the energy conservation equation2. The mass conservation equation, also known as the continuity equation, is expressed as:
Boundary conditions are the conditions that the variables in the calculation domain must satisfy at the calculation boundaries; they are a prerequisite for solving the governing equations. In this model, the boundary conditions are set as follows: Inlet boundary: The inlet type is set to velocity-inlet, with a velocity of 16 m/s and an inlet pressure of 4600 Pa. Outlet boundary: Both the exhaust outlet and the ash outlet are set as pressure-outlet types; since they are connected to the atmosphere, the relative pressure is set to 0. The gas backflow coefficient is set to 1. Other wall boundaries: Set as stationary, slip-free walls, with the standard wall function used to approximate the grid points near the wall. The initial conditions for the cyclone separator used in this simulation were all determined based on actual operating conditions, as follows: the inlet velocity of the cyclone separator is 16 m/s, the temperature is 733 K, and the pressure is 4600 Pa. To match the actual situation, a component transport model was activated when simulating the flue gas; the components of the flue gas along with their volume percentages are shown in Table 2.
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