Cyclone Separator Challenge
AIM:- To perform analysis on cyclone separator and calculate the separation efficiency and pressure drop.
Theoritical Background:
Cyclone Separators
Cyclonic separation is a method of removing particulates from an air, gas or liquid stream, without the use of filters, through vortex separation. Cyclone separators or simply cyclones are separation devices (dry scrubbers) that use the principle of inertia to remove particulate matter from flue gases. Cyclone separators is one of many air pollution control devices known as precleaners since they generally remove larger pieces of particulate matter. This prevents finer filtration methods from having to deal with large, more abrasive particles later on. In addition, several cyclone separators can operate in parallel, and this system is known as a multicyclone.
Cyclone separators are generally able to remove somewhere between 50-99% of all particulate matter in flue gas. How well the cyclone separators are actually able to remove this matter depends largely on particle size. If there is a large amount of lighter particulate matter, less of these par0ticles are able to be separated out. Because of this, cyclone separators work best on flue gases that contain large amounts of big particulate matter.
Empirical models used to calculate the cyclone separator efficiency
1. IOZIA AND LEITH MODEL
Iozia and Leith (1990) logistic model is a modified version of Barth (1956) model which is developed based on force balance. The model assumes that a particle carried by the vortex endures the influence of two forces: a centrifugal force, Z, and a flow resistance, W. Core length, zc and core diameter, dc are given as
2. LI AND WANG MODEL
The Li and Wang (1989) model includes particle bounce or re-entrainment and turbulent diffusion at the cyclone wall. A two-dimensional analytical expression of particle distribution in the cyclone is obtained. Li and Wang model was developed based on the following assumptions:
• The radial particle velocity and the radial concentration profile are not constant, for uncollected particles within the cyclones.
• Boundary conditions with the consideration of turbulent diffusion coefficient and particle bounce re-entrainment on the cyclone wall are:
3. KOCH AND LICHT MODEL
Koch and Licht (1977) collection theory recognized the inherently turbulent nature of cyclones and the distribution of gas residence times within the cyclone. Koch and Licht describe particle motion in the entry and collection regions with the additional following assumptions:
• The tangential velocity of a particle is equal to the tangential velocity of the gas flow, i.e. there is no slip in the tangential direction between the particle and the gas.
• The tangential velocity is related to the radius of cyclone by:
uRn = constant.
A force balance and an equation on the particles collection yields the grade efficiency ηi.
G is a factor related to the configuration of the cyclone, n is related to the vortex and τ is the relaxation term.
4. LAPPLE MODEL
Lapple (1951) model was developed based on force balance without considering the flow resistance. Lapple assumed that a particle entering the cyclone is evenly distributed across the
inlet opening. The particle that travels from inlet half width to the wall in the cyclone is collected with 50% efficiency. The semi empirical relationship developed by Lapple (1951) to
calculate a 50% cut diameter, dpc, is
The efficiency of collection of any size of particle is given by
Geometry:
The geometry of Cyclone Separator is imported in to the SpaceClaim as shown below
We need to extract the fluid volume by selecting the inlet and outlet edges to obtain the below geometry
Meshing:
Fluent Setup:
Solver: Steady State solver
Type: Pressure based
Model: k-epsilon RNG, Swril dominated flow, Standard wall function
Injections:
Type - Surface injection
Material type - Antracite
X-velocity - 3m/s
Diameter - varying from 1e-6 to 5e-6
Flow rate - 1e-20 kg/s
Performance analysis on a given cyclone separator model by varying the particle diameter from 1 μm to 5 μm
Case 1a: Particle diameter = 1 μm
Residual plots:
Velocity Contour Pressure Contour
Case 1b: Particle diameter = 3 μm
Residual plots
Velocity Contour Pressure Contour
Case 1c: Particle diameter = 5 μm
Residual plots
Velocity Contour Pressure Contour
Separation Efficiency:
Separation efficiency is defined as the ratio of concentration that has been removed from the feed stream to the initial concentration in the feed stream. The separation efficiency is given by the formula.
TABULATION:
The results of the above 3 cases are tabulated below
Performance analysis on a given cyclone separator model by varying the particle velocity from 1 m/sec to 5 m/sec
Case 2a: Particle velocity = 1m/s
Residual plots
Velocity contour Pressure contour
Case 2b: Particle velocity = 3m/s
Residual plots
Velocity contour Pressure Contour
Case 2c: Particle velocity = 5m/s
Residual Plots
Velocity Contour Pressure Contour
TABULATION:
The results of the above 3 cases are tabulated below
Observations:
1] When the diameter of the particle varies from 1 μm to 5μm by keeping the flow velocity constant of 3m/s the separation efficiency increases .
2] As the velocity of the particle varies from 1m/s to 5m/s by keeping the particle diameter constant of 5μm the separation efficiency increases.
3] Increasing the velocity of particle causes high pressure drop.