Week 8 - Simulating Cyclone separator with Discrete Phase Modelling
Aim - Perform an analysis on a given cyclone separator model by varying the particle diameter from 1 μm to 5 μm and calculate the separation efficiency in each case. Discuss the results. [Use both the velocity's as 3m/sec.
Cyclone Separator: Cyclone separators are separation devices that use the principle of inertia to remove particulate matter from flue gases. Cyclone separator is one of many air pollution control devices known as pre-cleaners 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 multi-cyclone.
It is important to note that cyclones can vary drastically in their size. The size of the cyclone depends largely on how much flue gas must be filtered, thus larger operations tend to need larger cyclones. For example, several different models of one cyclone type can exist, and the sizes can range from a relatively small 1.2-1.5 meters tall (about 4-5 feet) to around 9 meters (30 feet)—which is about as tall as a three-story building.
Working: Cyclone separators work much like a centrifuge, but with a continuous feed of dirty air. In a cyclone separator, dirty flue gas is fed into a chamber. The inside of the chamber creates a spiral vortex, similar to a tornado. This spiral formation and the separation is shown in the Figure below. The lighter components of this gas have less inertia, so it is easier for them to be influenced by the vortex and travel up it. Contrarily, larger components of particulate matter have more inertia and are not as easily influenced by the vortex.
Empirical models for Cyclone Separator Efficiency:
Iozia and Leith Model:
Iozia and Leith 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 flow resistance, W.
The collection efficiency i of particle diameter dpi can be calculated by
Li and Wang Model:
The Li and Wang model include 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.
Koch and Licht Model:
Koch and Licht 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.
Lapple 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 to calculate a 50% cut diameter, dpc, is
Applications:
- Chemical and Petrochemical Processes
- Industrial, Metallurgical and Power Generation
- Food & Pharmaceutical
- Cement Industry
Cases
With varying the particle diameter, at a constant velocity at inlet the flow is simulated. separation efficiency is found out.
With varying the velocity at the inlet, at constant diameter of the particles, the flow is simulated. separation efficiency and pressure drop in the cases is found out.
Case setup
geometry
import geometry in SpaceClaim.
extracted volume
Mesh
Setup
General setting
- Solver type: pressure based
- velocity formulation: Absolute
- time: steady state
- gravity enabled with the y-axis value -9.81ms-2
Discrete phase model
- Interaction with continuous phase enabled.
- tracking parameters
- max. no. of steps: 50000
- step length factor: 5
Case 1
a) Velocity = 3 m/s. Particle diameter = 1 micro meter
Boundary Condition
Run simulation for 600 iterations
Seperation efficiency = No: of particles trapped/No: of particles tracked
Seperation efficiency =333/378=0.8809=88%
Pressure Drop =26.685-(4.39211+2.293)=20 Pa
Case 2
speed -3m/sec and dia -3 micrometer
results
Seperation efficiency =339/378=0.8968=89.68%
Pressure drop=24.059-(3.177+3.576)=17.306
Case 3
speed -3m/sec and dia -5 micrometer
sepration Efficiency = 259/378=0.6851=68.51%
Pressure Drop=23.99-(3.19+3.52)=17.28pa
Case-4
diameter=5micrometer and speed=1 m/sec
sepration efficiency=279/378=73.80%
Pressure drop = 2.8789-(0.4348+0.19845)=2.24 Pa
Case 5
diameter=5micrometer and speed=5 m/sec
Sepration efficiency=277/378=0.7328=73.28%
Pressure drop =69.384066-(9.512623+9.9166704)=49.95=50Pa
CONCLUSIONS:
| Si No | Cases | Efficiency(%) | Pressure drop(Pa) |
| (1) | 3m/s, 1Micrometer | 88 | 20 |
| (2) | 3m/s, 3Micrometer | 89.68 | 17.306 |
| (3) | 3m/s, 5Micrometer | 68.51 | 17.28 |
| (4) | 1m/s, 5Micrometer | 73.80 | 2.24 |
| (5) | 5m/s,5Micrometer | 73.28 | 50 |
the results with the variation in diameter and celocities are shown in the table