A CFD Study of Industrial Double-Cyclone in HDPE Drying Process

Abstract

Double-cyclone in fluidized bed drying is an important equipment which reflects the conditions of drying in HDPE slurry process. Cyclone is an important unite of fluidized bed drying in order to move the solid particles outward to its wall. Therefore, flow pattern created in fluidized bed will affect industrial cyclones installed in dryer for dust removing. Pressure drop of the cyclones is an effective parameter represents the drying behavior. Substantially, geometry of cyclone, inlet flow rate of gas, density and particle size distribution (PSD) can affect the pressure drop value. Fluidized bed hydrodynamic regime is very complex and must be understood to improve fluidized bed operations through theoretical, industrial and CFD study of double-cyclone. Pressure drop is introduced as parameter related to the cyclone efficiency can be calculated with ANSYS Fluent software in the Eulerian-Lagrangian framework with RNG k-ɛ turbulence model used as a mathematical method. Proper pressure drop concluded from industrial experiments and CFD calculation shows good fluidization of HDPE particles in the bed of nitrogen and powder to reach the best fluidized bed situation and suitable quality of HDPE powdery product. Keywords:CFD; HDPE Particles; Double-Cyclone; Pressure Drop. Article History:Received: 28 July 2017Accepted: 01 January 2018 1-IntroductionHDPE Particles of fluid bed drying in the gas entering double-cyclone are subjected to centrifugal forces which move them radially outwards, against the inward flow of gas and towards the inside surface of the cyclone on which the solids separate [1]. The performance of cyclone is in a relationship with its static pressure drop between input and output [2]. The factors affecting the rate of entrainment of solids from a fluidized bed dryer named particle size distribution (PSD), terminal velocity, superficial gas velocity, particle density, gas properties and gas flow regime. Therefore, it is necessary to understand the gas-particle flow and separation characteristics of the cyclone.With computational fluid dynamics (CFD techniques), it is now possible to sufficiently calculate the pressure drop created in cyclone. Fluid flows have been mathematically described by a set of nonlinear and partial differential equations named the continuity and Navier-Stokes equation [3]. ANSYS Fluent solves conservation equations for mass and momentum and additional transport equations are also solved when the flow is turbulent. Different CFD calculation have been successfully applied by employing the related mathematic model to determine the features of gas-solid flow field for cyclones [4,5]. Turbulence models such RNG-based k-ɛ model which was derived using a statistical technique called renormalization group theory is one of the proper models in this field. In Fluent, the Lagrangian discrete phase based partly on the physical properties of dust particles and partly on the mathematical modeling with reasonable assumptions made to describe the particles transport in a fluid medium [6]....

The Secondary Flows in a Cyclone Separator: A Review

“…Time-of-flight models, in analogy to gravitational settling, propose that individual particles are only considered to be collected when they are present in the cyclone long enough for the inertia to touch the wall [9,14]. Leith and Licht [15] calculated how far the particles must travel to be considered to be collected by assuming the precondition that turbulence leads to a homogeneous particle concentration contact with the radial distance of the vessel wall, and they were able to estimate the separation efficiency of several cyclone configurations with considerable accuracy.…”

Study of the structure of gas flow іn a cyclone wіth іntermedіate dust removal

“…Зараз гідродинамічне моделювання газових потоків в апаратах різних конструкцій на основі CFDмоделювання широко вивчено [9,10]. Даний метод широко застосовується, наприклад, для оптимізації центральної випускної труби у великих циклонних сепараторах для цементного виробництва [11], досліджень характеристик великого промислового циклону Stairmand [12], досліджень структури газового потоку в залежності від конструкції вхідного і вихідного патрубка [13], оптимізації геометрії циклонів першої стадії, що використовуються в технологічній лінії випалу клінкеру цементного виробництва [14], дослідження гідродинамічних режимів роботи циклону для вловлення пилу поліетилену низького тиску [15], дослідження впливу високої запиленості газового потоку при температурах навколишнього середовища і підвищених температурах на роботу циклонних сепараторів [16].…”

The influence of the design of the upper cover of the cyclone on its characteristics

“…Currently, hydrodynamic modeling of gas flows in devices of various designs based on CFD modeling has been widely studied [8,9]. This method is used, for example, for the optimization of the central exhaust pipe in large cyclone separators for cement production [10], studies of the characteristics of the large industrial Stairmand cyclone [11], studies of the gas flow structure depending on the design of the inlet and outlet nozzle [12], optimization geometries of cyclones of the first stage, that are used in the technological line of clinker firing of cement production [13], study of hydrodynamic modes of IOP Publishing doi:10.1088/1757-899X/1277/1/012022 2 cyclone operation for capturing low-pressure polyethylene dust [14], study of the effect of high dustiness of the gas stream at ambient temperatures and elevated temperatures on the operation of cyclone separators [15]. In [16], numerical modeling methods were used to analyze the influence of operational and design parameters on the hydraulic resistance of a straight-flow cyclone.…”